In https://www.mediawiki.org/wiki/Topic:Vqx6zf3sjx6cv8kc a user reports 2 files that got "partially" moved by FileImporter. Only the description page was moved, but the actual image files are missing.
I gave one of the files a quick try, and it imported just fine in my local dev environment. Which means this might be a temporary issue, and hard or even impossible to track down. Next step should be to see if there is anything in the logs.
I was importing many files very fast so that may have been the cause of the problem. I never had problems like that before so if logs show nothing special its okay to close this and spend the time om something else. The easy solution is to delete the broken pages on Commons and try the import again.
Filepages are now deleted on Commons and the files are now imported with succes. No problems! So it was just a temporary issue.
Thanks for the update! We had a look but couldn't spot anything obvious. Let's see if something like this ever happens again. Please let us know if it does. Feel free to reopen this ticket or open a new one.