Q: "Disk Not Ejected Properly" error after EL Capitan goes to sleep and wakes up again.

Once again let me repeat what works for me. In energy saver set computer sleep to never. Un check "put hd to sleep when possible. I have 2 external hds. One is firewire 800 and one is sata via a OWC PCIe seta adapter. It workes for me in 10.9.5, 10.1 and 10.11.

Having contacted apple support and updated to El Capitan 10.11.4 (I was on 10.11.3) this seems to have resolved the problem (only three hours so far but looks promising.  During the conversation with Apple it was mentioned ' that there's a lot on this...' so I suspect Apple were fully aware of the problem in the previous update.  Unless it re-emerges later I suspect resolved.  I'd rather allow the mac to sleep when I'm not using it...

nealt2, this may be a solution for those using SSDs; it is worth noting that for spinning disks it is likely to result in shortened lifespan -- as, for example, they merrily continue running during the hours a user is asleep or otherwise absent. 

Angry again, some of us who continue to experience the issue (I am among them) are running 10.11.4.  Some of us who thought they had found a solution discovered many hours later that they had not as the unmounts suddenly returned.  I'll hope that your three hours turns into days and weeks, but I suspect it may not.

carmi_m, I understand your frustration, having had enough of my own on this.  It would be helpful if you provided information about the particulars of your experience.  What computer?  What drive or drives are you using.  When and how often does the issue appear?  What version of OS X are you running?  Have you tried any of the suggestions in this discussion that appear to offer some (temporary, in most cases, sadly) resolution?  In order to move toward a fuller understanding, some specific information would be of use.

Angry again, I don't want to jinx you but I suspect your success will be short lived. Like myaka said, I too am running 10.11.4 and I am also continuing to have this issue. For me, it's always when waking from sleep.

Well my G-Drive is waking from sleep again. The reason? Once again, it thinks it's connected to a USB 2.0 port, when it's actually connected to USB 3.0. This is very weird.

Kelly, My USB 3.0 GDrives show up under the "USB 3.0 Bus" on the main tree, but then under "USB 2.0 Hub" when I drill down a level...

Those G-Drives are USB 3.0 drives plugged into a USB 3.0 Hub, plugged into a USB port on my brand new iMac.

My two USB 3.0 drives have only ejected themselves once in the past 7 weeks. However, my Thunderbolt LaCie drive is STILL ejecting itself after waking the iMac from sleep. It's happened every day this week. It used to be ejected immediately upon waking, but now the trend is it ejects itself about 1-2 minutes after waking. I was less concerned when the iMac would wake up and the drive would just not be there, but now I really don't like that it ejects after everything has spun up.

Come on Apple. What is up???

Okay, well my MacBook Pro once again decided to place my G-Drive under the USB 3.0 bus, which means I'll likely start to have sleep issues again. To the people on this thread who were contacted by Apple, are they working on the problem?

Kelly, I submitted a bug report and after a few days, I got a response asking for a sysdiagnose report. I submitted one right away and then another a couple days later. I never heard anything back. It's been a couple weeks.

I'm still getting my errors daily. Nothing has changed.

(Off Topic - Has anyone else noticed how incredibly awful these discussion pages are to read and navigate on an iphone?)

I ran Disk Utility and it did not find errors but it said it updated my very old iomega drive. If it gives me the eject message again that I have gotten for about a week I will buy a new cable, Very strange as I have been using El Capitan for many months before this happened.

Okay guys, I just updated to Mac OS X 10.11.5 and once again my G-Drive is showing up under the USB 3.0 Bus. Getting ready to hit the hay. Let's see if the G-Drive wakes up later this morning. Fingers crossed.

I probably shouldn't get too excited, but this morning my G-drive was still listed under the USB 3.0 bus and it WOKE UP! That's one wake from sleep. Let's see if it keeps doing it.

I've now let my MacBook Pro go to sleep around a dozen times and I haven't had any problems with it waking up. And yes, it's still listed as being connected to the USB 3.0 Bus. Way to go Apple! I think you may have solved this problem. Curious to see how others are doing.

Thanks for posting, Kelly.

I am sometimes reluctant to update.  If 10.11.5 is working for you, that helps.

(My problem was slightly different. earlier in this thread.)