I have seen very similar behavior, and never resolved it but mentioned what I’d found here:
Frustratingly, the cutoff for what filesize was too big was never written in stone – sometimes a given ~1.5gb file would upload with success, other times it would (appear to) fail.
I had a theory that it had something to do with my /tmp or /var (lvm-)filesystem filling up since I discovered a given upload will eat up space on both. This didn’t seem to be the root issue for me (at least with the brief investigation I did) but maybe worth checking if it’s the case for you: PSA: File Manager uploads use both /var and /tmp space
My example watch-script is admittedly hard to read but the gist of it is a single upload temporarily stores three copies, like:
- /proc/1386416/fd/8 => /var/tmp/ondemand-nginx/USERID/client_body/0000000001 (deleted)
- /proc/1795862/fd/10 => /tmp/PassengerTeeInput-1l86ohu (deleted)
- /tmp/RackMultipart20260219-1795862-wimnh4.zip