A Microsoft file hosting and synchronization service.
I have come to the same conclusions as you have but to add to the list of fixes,
I have found that if you sync the library with OneDrive, instruct OneDrive to always keep the items on your device (obviously can trigger a large download) this also fixes the files in question. You can then safely use the "Free up Space" to remove them from your local drive. I looped through our previously migrated sites with this method and it fixed all of those libraries.
We also have confirmed it happens on files migrated from SharePoint 2013 on Premise using ShareGate that also have the issue.
Hello Jason,
The only problem is this will only fix the files on the local computer (at least it did for me). It doesn't actually upload the fixed file when you press 'Free up space'. I'm not sure why it continues to work locally but I am guessing there is a cached file somewhere. Curious if it was different for you.
-Justin