USB problem/Thunderbolt on Mac mini M4

Lose the extra cabling and adapters at the mouse and keyboard port. The USB keyboard and mouse don't require anything but a simple USB-A to USB-C adapter to connect to the ports on the back of the Mac mini. They are simple and affordable @ about $10 a pair on Amazon.

They look like this:

In fact, if your keyboard has USB pass-through you only need a single connection to the Mac mini. You can daisy chain your mouse through the keyboard. Unless I'm misunderstanding something here.

I think it is a physical hardware problem in my case— the rear ports do not provide a secure fit. Slight movement of a cable is enough to disconnect an external drive. In my case, I have a powered OWC 11-Port Thunderbolt Dock (with 2 drives attached) connected to a rear port. I've now tried 2 thunderbolt cables to connect the dock to the rear ports on the M4 Mac Mini and I've tried 2 of the 3 ports.* Both cables and both ports have disconnected with a slight movement of the cables (at the Mac Mini end of the cable). Both cables are new that came with products (i.e. external drive enclosures).

The last thing I'm going to check is to see if the insecure fit problem also exists with an Apple-branded Thunderbolt cable (iow, if the Mac Mini M4 doesn't play nice with non-Apple cables). I have a nearby Apple store, so probably will just take it in to have them see for themselves.

I'd suggest giving your cable the jiggle test to see if the physical port is the problem.

(*I haven't messed with the 3rd rear port because my Home directory is running on an external drive there; it also disconnected once, causing problems, and I'm leaving it untouched with my fingers crossed).

John Smiley wrote:

Update - Replaced the long USB extender cable with adapters with a single "high speed" USB-C to Micro-B Cable (no adapters) and have been using the rear ports without "disconnect" error for a few days.

FYI, people need to make sure the length of their cables do not exceed a certain length or there can be issues with transmitting data & staying connected. Not all cables or adapters work the same....it is usually best to stick with high quality cables & adapters as well, but even if they are from respected manufacturers they can sometimes have compatibility issues with some devices/computers.

Good job, hopefully that is a long lasting solution for you.

Had the exact same problem.... now solved. The information herein might help others with troubleshooting.

I have an M4 Pro Mac mini and an Apple Studio Display. Have 2 Apple keyboards. One about 7 years old (Bluetooth) and another about 13 years old (Model A1243). Both have the numeric keypad. The older one has a USB-A connector.

I prefer the older Model A1243 just for the feel of the keys. But it would work intermittently when plugged directly into the Mac mini or the studio display (used Anker adapters). The front ports on the Mac mini worked best, but still were intermittent. Very frustrating.

Also have an OWC Thunderbolt-4 dock. Eventually plugged the dock into the Mac mini. This dock has a USB type-A port. This dock also comes with optional software for ejecting disks connected. But per OWC:

"When you install this app, a driver is also included for the dock’s high-power USB ports. The driver enables use of the Apple SuperDrive and USB Keyboard on these ports, and should enable them to charge 1st, 2nd, and 3rd generation iPads as well."

Installed the dock driver and plugged the old USB keyboard into the Type-A port of the dock. The keyboard works perfectly! I've been using it for a couple of weeks.

So.... I am wondering if the issue has something to do with the power (or voltage?) being provided through the new generation USC-C and/or Thunderbolt ports for old USB devices. Note that OWC dock has its own power supply.

Anyway, hope this info helps.

It’s actually the USB consortium that’s confused everyone. A Thunderbolt cable whether 4 or 5 is certified by Intel to meet the spec, so that means all USB standards up to USB4 (Tbolt 3 cables support USB 3.2).

USB cables are not certified and often not even marked. Look at the charging cable that came with your recent MacBooks…C to C, no markings and it only passes power, no data.

To figure out what a USB C-C (or C-A, C-B, etc.) cable can support I connect a peripheral using that cable and see what System Report displays for the USB connection. The cable that came with my Samsung T7 shows 10 Gbs rate, which is 3.2 gen2 as advertised. I have other USB-C cables that when used with the T7 show only 5Gbs data and one that shows only a USB 2.0 connection!

So when I need spares or something longer, I’ve bought TB4 cables. At least I know they will provide the maximum speed and power for any USB peripheral I might use.

If USB-C to USB-A adapters work

in the front, but not in the back, I’d suspect that some piece of equipment was not standards-conformant. I couldn’t say whether that would be the TB4 ports or the adapters, but if they are third-party adapters, you might want to try a different brand. I’m guessing that Apple tests interoperability a bit more than third-party adapter vendors might.

I know this will be extremely annoying for some of you to read, but really do invest in quality cables. I've had similar issues with an audio interface. It was sometimes powered and working and sometimes simply not seen by the Mac Mini. Swapping the cables didn't yield satisfactory results until I swapped it with an Apple cable and suddenly no more issues. I now invested in a high quality audio cable to further limit latency problems and haven't had any issues since.

I've since experimented with different cables, and reached the conclusion that they are the source of the strange behavior. The interface requires simultaneously “high” power and data transmission, which I expect is the same of some usb hubs and drives that you guys are having problems with. The thing that is strange is that the cable is not outright rejected, but the Mac Mini seems to be throwing a coin to decide whether it will accept or not accept the device on a particular boot. It seems like a typical case of something the device wasn't designed to deal with at all and thus leads to some sort of “undefined behavior.”

Look carefully at the specs of the cable that you require, swap the cable with a better one. I know this sounds like “you're holding it wrong,” but it is what it is.

Update - Replaced the long USB extender cable with adapters with a single "high speed" USB-C to Micro-B Cable (no adapters) and have been using the rear ports without "disconnect" error for a few days.

I had the same problem on new mac mini m4 : 1 apple keyboard and 1 optical mouse, both wired and fitted with a simple usb to usb-c adaptor, and connected to any of the front usb-c or rear thunderbolt slots had them disconnected after a while. Using a non-powered usb hub didn't change this.

After lots of tryouts the following works (but don't ask me why) : optical mouse connected to front usb-c slot and apple keybord connected to a non-powered hub connected to rear thunderbolt port. Doesn't work without the hub !

See hardware usb values included

This looks like an issue with both the quality of the cable and also length (because of Thunderbolt which is more sensitive to cable lengths than USB).

How long are the cables in the back? Have you tried 3 feet or shorter (1m or less)? Use Apple cables if possible.

Had two USB drives plugged into rear USB-C ports, one an SSD with a short cable (USB-C to USB-C) used as Time Machine **, the second was a USB-A through a USB-A to USB-C pigtail with an extended, longer USB cable to the 2nd disk drive. The OS was flagging dismounts with the TimeMachine drive. When I moved the 2nd cable to the front USB-C, the dismounts with the still rear attached TimeMachine SSD went away. IMHO the rear connectors are underpowered to be fully utilized.

I used the exactly same usb to usb C connector and the problem is same with the thunderbolt ports,You need to manually remove the usbc from the thunderbolt and reinsert it then only it works again

After much trial and error, the USBC issue is definitely on the rear ports and happens during sleep. I've had constant disconnects of hard drives connected directly (I've tried 3 different drives), usb hubs (I've tried 3, the last one is powered). Plugged in the front, I've not had any problems. It manifests itself when the Mac mini goes into sleep mode. I get the message that my Time Machine drive was ejected incorrectly. Hopefully this is a software bug; not good!

I have a Mac Mini M4 Pro and have seen the following. I have an external NVMe enclosure on the Thunderbolt port in the back. That drive stays connected!

I have another external enclosure with old HDD drives for my Time Machine backup connected on the back port via a USB-C to USB-B cable. That enclosure does NOT stay connected and I get a message every morning that my Time Machine was not ejected correctly.

I have moved it to the front port and so far it has been staying connected, but I will monitor for a few more days.

In summary I am experiencing USB 3.x devices on the back ports loosing connection. TB devices on the back ports remaining connected.

drew_como wrote:

With this thread gaining traction over the last few weeks, I really hope that someone from Apple takes notice.

Apple doesn't normally participate in these forums, except to moderate them. You might want to try to raise the issue through Apple Support or through Apple's Feedback page.

I would suggest including as much specific, helpful information as you can, about

• Which combinations of devices and ports don't work
• Which do

Although most people reporting problems in this thread are having problems with one set of ports (front or back), the people who are having problems with the front ports may be having a different problem (as far as root causes are concerned) than the people who are having problems with the back ports.