ProRes 422 Rendering Codec Causes Excessive SSD Wear and Slow Exports in Final Cut Pro

I have a project using multi-angle cameras: one at 8k24p, (8192x4320) the other 4k59.94p (3840x2160). The 8k is in Canon Raw LT (CRM) format (~1TB), the 4k is in XF-AVC (~200GB). The length of project is ~1.5h. I'm using a 48gb M3 Mac MacBook Pro. Using the latest Final Cut Pro 11. The project settings are set to 4k24p, and the MultiCam and sync-audio clips are all set to 4k24p.

I had two different projects using the exact same configuration. I did all my edits, and exported the first one using the 3840x2160, HEVC 8-bit, Apple Devices preset, allow segmentation. ( It was able to encode in <2 hours.

Then, I created a new library for the 2nd project. I did all my edits, and noticed that it was taking much much longer to export. I let it run overnight, and it was only not even 10% done. I run iStat Menus, and noticed that I Final Cut/related apps were using over 32Gb of physical ram. Memory pressure was high - over 80% - and was using around 20GB of swap. I also noticed that it was alternatively reading/writing over 500MB/sec to the SSD, and this was all to the swap file. In fact, overnight, the SSD wear level went up by 2-3%, and only the export was still only 10%.

I couldn't figure out what was going on. I was concerned about the wear on the internal SSD, so I thought - I'll just boot the MacBook from an external drive - let it wear out an external SSD instead of the non-replaceable internal SSD.

So, I set up a fresh install of MacOS 15 on an external drive (8TB WD SN850X, using OWC 1M2 enclosure) - copied all the originals and library to it, and started the export. I noticed it was going as slow as before.

I know my earlier project worked much faster, and was tearing my hair out trying to figure out what the difference once. On a whim, I looked at the project settings. I saw a difference in project's Rendering Codec: other project was using ProRes 422 LT as and this one was using ProRes 422. Sure enough, after I switched to ProRes 422 LT - and retried the export it was able to export in <2 hours, with no excessive RAM usage, no swapping!!

I don't know why the Rendering Codec would affect sharing the project. From my understanding, it should only help with playback while in the timeline. Note: I also tried this by sending it to Compressor -- same problem. I thought it was perhaps due to Canon Raw LT source - in struggling to figure it out, I eliminated that because I also tried relinking the Canon Raw LT files to the "Optimized" ProRes files (4TB!) - and even the proxies directly - same effect. The common thread was using ProRes 422 (not LT) as project rendering codec.

So, I figured this out - this was more of a cautionary tale for anyone that may stumble upon this message in the future. If anyone at Apple sees this, I would check this out and see if this is a bug.

Thanks!!!

[Re-Titled by Moderator]