Universal control intermittently works

Universal Control apparently stops working for any of several possible reasons. Most common: whenever either system goes to sleep (for whatever reason). To have get Universal Control to reconnect, on the Mac with the keyboard & mouse, make sure that Preferences -> Displays -> Universal Control "Automatically reconnect ..." is checked. And wake up both systems.

If you have a System Preferences window open on the Mac, a little picture of your iPad should show up next to your Mac display there when Universal Control reconnects (re-Links). If you don't see it show up there after, say 10 seconds, go to the Add Display dropdown. You should see the name of your iPad under a sub-heading called "Link keyboard and mouse". Click on the name of your iPad and a checkmark should show up there, indicating that Universal Control between your Mac and iPad is linked now.

[The name of your iPad may also appear below the subheading "Mirror or Extend to" in the Add Display dropdown. Do NOT click on that. If you do, your iPad will become a Sidecar display for your Mac, and Universal Control will not work with your iPad until you turn Sidecar off.]

If you're not seeing the name of your iPad in the Add Display dropdown on your Mac whenever both systems are both awake, then there's a problem with the Mac and iPad communicating with each other either via WiFi or Bluetooth (Universal Control uses both) or authenticating their communication (using the same Apple iCloud ID), or something (often that would be a VPN or firewall) is interfering with their communication.

To tell when it's working (and when it's not) add Displays to your main menu bar:

System Preferences -> Dock & Menu Bar -> Displays -> Show in Menu Bar always

Its icon will look like some kind of split screen when it's working, and like a plain monitor when it isn't.

If Universal Control not working, but the iPad is available, you should see it available as a choice you that you can "Link keyboard and Mouse to". Don't go into Display preferences and click on the iPad for Add Display (that'll start up Sidecar instead of Universal Control).

.... Keeping an eye on that Display icon in the menu bar, I think I may be detecting a non-random pattern for when the Universal Control stops working ... maybe.

When it stops working have you tried just going to Display preferences and clicking on the Add Display button then clicking on the Universal Control with iPad part (if there).

Just adding another voice that it is really inconsistent as for initiating connection or reconnecting. What helped several times was to force stop the Universal Control process in the manager and wait a minute or two. But it didn’t always help. Could it be that the system does not regard the feature as high priority and only checks on it every once in awhile?

Going into my iPad's settings and toggling WiFi seems to fix it so it reconnects. Sometimes.

When Universal Control doesn't work, I try to use some other Continuity features as workarounds. But least some other Continuity features, like Handoff, and Universal Clipboard don't to be working as well. Still trying to figure out which work vs. which don't (besides Universal Control). Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

Meanwhile, according to a different Discussion thread, while Universal Control can't wake up a sleeping Mac any more than it can wake up a sleeping iPad, but UC Auto reconnect *does* seem to work between Macs. universal control won't wake display sleep - Apple Community

So after spending multiple-days trying to figure out how to force UC to reenable, I've determined that it's voodoo. Once either/both the Mac or iPad goes to sleep, the connection is lost. Once both devices are awakened, it may take a few minutes (or more) but they'll eventually connect again.

This is not a good user experience but at when it does work, yeah, it's pretty awesome.

I don't often use other Continuity features, but after UC goes down and while it's not reconnecting, I went and tested a few other Continuity features. While Sidecar and Handoff appear to work, these other Continuity features do not work for me:

Continuity Camera (Mac tries to use iPad's camera)

Continuity Markup (trying to use markup on iPad within an open document on the Mac)

Continuity Sketch (trying to make a sketch on the iPad to insert in a Mac document)

Universal Clipboard (cutting and pasting between Mac and iPad)

... and, yes, I checked. Both systems meet all the Continuity requirements for all of those features.

I'd appreciate it if someone else can test these Mac -> iPad Continuity features, maybe under different conditions?

While your t-shooting is spot on, the problem is that the connection still drops and at least in my case, my iPad doesn't show up as an available display or something to connect to via universal control. The fast forward a few minutes, maybe an hour, maybe multiple hours and voila! there it is and UC just magically starts working again.

The fact that there's no consistent behavior with connections or disconnnections - despite every thing being configured correctly, tells me this is still a feature that needs additional baking.

I'm running on the same setup with the exception of my Mac being smaller. It will handoff just fine, but only stays on the iPad for about 5-10 minutes if I'm lucky. It feels like the Ipad memory gets overloaded or something of that nature. I'm not a guru by any means so that's the best way I can describe it. Running macOS Monterey 12.3.1 MacBook Air M1, 2020 and iPad Pro 129 on iPadOS 15.4.1.

You're not alone. I'm having the same problem except that going into my iPad Pro's settings and toggling the handoff and cursor/keyboard does seem to fix it. Sometimes.

Very frustrating.

...and that little icon helps me not go crazy banging the cursor against the monitor sidewall checking every half a minute if UC is already working or not. Great tip :)