Late 2015 iMac 5K Freezing

Since you're using this computer for your work you must have a backup computer right? If not that's a poor business decision. Don't mean to sound unsympathetic but that's the way it is. You've already been told that, based on the small portions of the reports you posted, you have a hardware problem, likely a GPU issue and that you need to take it in for service. While it's there you'll have to use your backup computer. Wise choice purchasing AppleCare.

You mentioned you have AppleCare, I'd suggest calling them and getting help.

The graphics processor or some other internal component is defective and must be replaced under the warranty, at no cost to you.

I understand you're frustration, but what do you expect of us? You have a hardware issue that needs to be fixed by Apple. There's nothing that can be done over the internet.

I'm in a similar situation. 2015 Macbook Pro Retina, all the latest software, all up to date. I was experiencing the same behavior while using Final Cut Pro X. Never any other time. It would happen seemingly randomly, while placing effects or simply playing the timeline. My cursor turned into a beachball, and the Mac OS X GUI would become completely unresponsive. The clock stopped moving but I could move the mouse around the screens. The audio continued to play in the background. If Spotify was playing, it would go to the next track. Notifications would still make their sound. Hard shutdown is the only remedy.

I performed all kinds of software troubleshooting steps, including clearing caches, zapping PRAM, SMC reset, safe mode, single user mode, reinstalling FCPX, reinstalling codecs, switching from Firefox to Chrome, plus a few other things I can't remember. So my conclusion was that it was a hardware issue. I took it in for repairs and showed them the kernel logs that clearly show a gpuRestart / GPU Reset at the times the freezes occurred. The repair tech agreed it was a hardware problem and replaced the logic board.

Guess what? It wasn't the logic board. The problem continued pretty much immediately. So this was infuriating because at that point I was on my own. Apple wasn't going to help me with a software issue, besides the steps I already took. I'm not too keen on resintalling the OS; I don't think that would help anyway. Back to troubleshooting....

Hmmm. I use the machine at work and at home, but it never crashed there. In fact, the only time it ever crashed was when my OWC Thunderbay was connected, while at work. Even when the only thing connected was the (brand new) Thunderbay – no displays or drives – it would have these GPU resets. I have a Thunderbay at home as well, so I really didn't consider that could be the issue. Lo and behold, I thought maybe I'd try a different Thunderbolt cable. Aha! It didn't crash for a solid week! It WAS a hardware issue: the cable! Alas , perhaps not. I'm back on the internet today, searching for answers because it happened twice. Maybe it was the OWC cable to some degree? Why else would the system be solid for a whole week? But now I'm certain that something else is at play here.

The whole situation is baffling and absolutely pi**ing me off. What else should I and the OP be trying? I really wish this high priced hardware and highly acclaimed software would "just work." Maybe I should just go ahead and discard this Macbook and use a $2700 backup machine? Because really, who doesn't have one of those.

That would be great, if Adobe allowed use of CC on multiple machines. Not a really practical solution for most of us.

I'm having the exact same problem, but it arose when I updated to Sierra.

Did you solve your problem?

Yes it did. OS Sierra eliminated most of the issues I was having with Yosemite and El Capitan too.

Ok, so it's the opposite for me... Sierra brought on this freezing issue for me.

Same problem here ... can't even restart in safe mood. Will resort to Apple tomorrow. Very Frustrating give it's a 2 week old machine.

I need to revise what I said earlier. It's happening again, and I haven't installed anything new since upgrading to Sierra. Any software updates in the App store have been done, but I haven't run them. So, based on the error reports, it seems there is a real issue with the GPU (AMD Radeon R9 M390).

I have a Late 2015 27in. iMac. Since updating to Sierra I've crashed/frozen every morning at least once, sometimes twice. Just browsing a webpage, nothing special, and the cursor just freezes. Can't do anything, Have to shut down. This morning, after restarting, I could move the mouse around but it wouldn't select anything I clicked on in Safari. I could click on another window. So I quit Safari, re-opened and it works.... for now. I've talked to Apple twice and they've done the usual screen share, looking for extensions, etc. I have none. Pretty clean computer. Final Cut crashed a few days ago, too. Just closed up on a mouse click somewhere. I had NO trouble with this computer until I moved to Sierra. They have to know there are problems....they're all over the web in posts. I assume Apple has people who do nothing but read these things all day. It's very frustrating. Taking the computer in is the last thing I want to do and I have little faith it would help. I think this is a total software issue with Sierra and they're trying to figure it out. We'll see 10.12.1 soon, I hope.