i have similar problem, crypt remote on 1fichier, some files cant be uploaded, no matter how many retries. Always upload response not found for those specific files.
No anything else in -vv log, just these.
But i’ve found a WA: try to upload those files on a mount, it will fail, then rename the file to something like this: x, q, r… just a character, then it will be uploaded, then rename it to the original filename.
Maybe crypt backend (set to encrypt filename) creating some incompatible filename, but if you force it to re-create/re-encrypt the filename it creates a compatible one?
It’s a long standing problem for the same files: Crypt remote problems, limitations?