stable proftpd 1.3.6 has problems with tls13, so we add the disable-tls13 flag for rclone to refuse tls13 proposals and downgrade connection to tls12. if you run your client without the flag and it breaks, we will know for sure that it helped in your case.
unstable proftpd 1.3.7a made improvements with tls13 so we don't need that flag (i guess hetzner has it, at least i don't need the flag).
tls-cache-size was an attempt to mitigate authentication of tls ftp data streams by the tls preshared-key from the tls ftp command stream optionally requested by some ftp servers.
this attempt has not been confirmed yet, i guess this will need some tls changes on golang side to be fully resolved.
as we can see your ftp server does not request it (as of the time of last probe).
besides tls changes this branch has modtime patches to make rclone pick optional MFMT,MDTM,MLSD commands if advertised by ftp server (so rclone ftp can read and set modtime),
though in your case this made things worse by uncovering a quirk with your ftp server settings, so we added flag --ftp-disable-mfmt to revert this feature.
also this branch has patches changing the way rclone handles timeouts between ftp data and control streams.
this change can improve uploads of large (>1G) files preventing spurious Close timed out (reported as EOF for TLS streams) errors.
this part is unfinished and needs thorough testing and polishing. I don't know if it helped in your use-case. (though it helped here FTP Upload Timed Out - #9 by ivandeex)