iMac keeps shutting down while rendering

Late 15 iMac. 4.2, 32gb RAM.

It freezes, shutting down, and reboots. A reboot didn't give me a crash report. After shutting down and after freeze (I had to reboot manually), I was given a crash report. It was either Mojo from Red Giant or kernel panic. I deleted Mojo, and was then served with kernel panic.

I have 2x16GB from OWC, leaving to slots open. I have also tried with original 2x4GB leaving me with 40GB. Still shutting down. Is my iMac unstable with 2x16GB and to slots open?

I tried exported 400 images in Lightroom to test. Fan was going strong, but didn't shut down. Rendering in FCPX didn't activate the fan worth mentioning. It was there, but not as strong as exporting images in Lightroom. I tried render h.264 and proves 422. After around 50% it shuts down. It is worth mentioning that it was a 21 minute long film, around 1TB library. 4K (Canon 5D mark IV and GoPro 6).

It doesn't seems like my iMac shuts down because overheating, because temperature is fine. I have plenty of storage.
I now it might be millions of reason for this, but I have never experienced it when running FCPX, especially not when fan is barely running.

Any idea?

If I were very frustrated and wanted to remove all possible app related issues, I'd...

First, I'd download "Remove FCS" from Digital Rebellion (dot com) to totally wipe FCPX and Compressor from my system, reboot the whole system, launch the App Store to reinstall both, reboot again, and make sure Background rendering in Preferences was turned OFF and NEVER turn it back on.

Then I'd run Disk Utility's First Aid on all drives.

Then I'd run Final Cut Library Manager and delete all render and cache files from all Libraries at once.

Then I'd run a test. If there's still a problem, could be corrupted media.

Done it, but still shuts down while sharing the file. I tried sharing on my MacBook Pro. Not a problem at all. So there is something wrong with the iMac.

I removed the two 2x16gb RAM from OWC and inserted the standard 2x4gb RAM from Apple. It works. So trouble is either OWC ram, or 2x16GB. This is the THIRD time OWC RAM generates trouble.

That is very unusual for OWC RAM. I've used it exclusively for decades and never had an issue. It could also be something on the logic board that is failing when having to deal with too much physical RAM. I'd have an Apple retail store check that machine out.

And this all assumes you're tried a fresh OSX install, and have more than 20% of each drive's capacity left as free space. Yes, those could cause the same symptoms.

So something RAM capacity related, is safe to say.

It is working fine when working in AE, Photoshop and Lightroom. When shutting down (while sharing in FCPX) the fan didn't work much. But is sharing RAM-related? I can't see the connection.

No, I haven't done a clean OSX-install (installing Logic Pro X instruments is hopeless. That's why I haven't done the clean install yet). 60% free space. I want to try 4x8gb, but OWC won't swap them for the 2x16gb, so I need to buy the 4x8gb, and then get a rebate on the 2x16gb (which isn't much).

We recently had a similar issue with our RAM causing trouble and making machines shut down during exports and renders. Turns out it was a bad OWC RAM chip.

The other thing that I recently had to deal with was my computer shutting down randomly, no specific action would recreate it but it kept happening. Got on the phone with Apple, had their engineers on the case, and it turns out what was causing the trouble was the Dropbox Finder Integration. Apparently this is a known issue and Apple has been in contact with Dropbox to have them try to fix it and Apple is also working on a OS update to address it, but if you use Dropbox and have the Finder integration app installed you should try only using it when absolutely necessary. (Though this specific case looks like you've narrowed it down to the RAM)

No Dropbox in Finder. My iMac also just shuts down for no reason when sharing. And when it did, I didn't get a note after reboot telling me that there was a problem. Before uninstalling Mojo, I was told there was a problem with Mojo. After uninstall, a got a not the there was a kernel panic. But randomly I didn't get note. Just a clean, reboot from a clear blue sky.

Happens to me as well - but ONLY when i have been using Safari, never otherwise. I need to restart and avoid Safari when rendering. I have an iMac 27 late 2014, Intel i7, 32 GB RAM Kingston x4 DDR3 1600 MHz. Catalina 10.15.7, FCPX 10.5.2.

Erik_Sweden wrote: Happens to me as well - but ONLY when i have been using Safari, never otherwise. I need to restart and avoid Safari when rendering. I have an iMac 27 late 2014, Intel i7, 32 GB RAM Kingston x4 DDR3 1600 MHz. Catalina 10.15.7, FCPX 10.5.2.

If MacOS does an uncommanded shutdown when under load, that is a system-layer issue, not something that can be fixed in FCP.

Possible areas to examine: 

- Make sure all drives have at least 20% free space
- Use Activity Monitor to watch memory pressure while the tasks are running. On the memory tab look at the memory graph. It should be green, not yellow or red.
- Run this command from terminal to inspect what 3rd-party kernel extensions are in use. A bug in any kernel extension can cause MacOS to crash, hang or reboot spuriously:

kextstat | grep -v com.apple

- Run this command (exactly as below) from terminal for about 60 sec, then stop it with CTRL+C. It will list any shutdown caused by a kernel panic over the past 7 days:

log show --predicate 'eventMessage contains "panic"' --last 7d

- Run Apple diagnostics. They are very lightweight so an error-free pass means nothing, but it's easy to run and if it finds something that is significant. The Apple Genius Bar has access to much more rigorous bench diagnostics which can be run for several days if needed. Those are more likely to find an intermittent or incipient problem:  support.apple.com/en-us/HT202731