FCP project files on external SSD show "Modified File" error

Thanks for that info. You have done the right thing: SSD is formatted APFS, and the OWC hub is a quality product.

The thumbnails should never flash red. Is the USB-C cable from the Crucial X8 to the OWC hub the original OEM cable from Crucial? Sometimes SSDs are very sensitive to cable type.

Can you use the free Blackmagic Disk Speed Test (available on Mac app store) on the X8 SSD to check the read/write rate?

If you can get prepared to gather some additional troubleshooting info, I can examine that. In terminal, enter this command, then enter your password, but do not press the final "enter."

sudo log show --last 90s > ~/Documents/LogShow_90s.txt

When the thumbnails flash red, immediately go to the terminal session and press "enter." That will gather the previous 90 seconds of the Mac system log in the file LogShow_90s.txt. It is very verbose but I'm experienced filtering through through. In Finder, right-click on that file and compress it, then upload it to the URL below.

https://we.tl/r-bAQQU51kIi

To help us understand the cause, could you please tell us the drive type and format of the hard disk holding that file? Just to confirm, is it a directly-attached SSD? Is it formatted ExFAT, HFS+ or APFS? If you aren't sure, just select that drive in Finder and do CMD+I.

Are there any proxies for that media, or just the original media?

Do you have any cloud-based or backup services that have access to those files, such as Dropbox, Google Drive, etc?

I tried to reproduce this by manually modifying the media file attributes using the command-line "touch" and "SetFile" utilities to change the file's modified date and creation date. None of those caused the problem -- but this was on APFS.

I could start blindly testing other things, but if you could provide the above info, that would save some time.