Thanks for your feedback!

Thanks! I tested the version you sent me, and it is working fine both without and with BLOCK_SIZE set, both with and without my WinSCP.ini.

Interestingly, I had trouble reproducing the original issue with v 5.21.x at first, even with BLOCK_SIZE set – I was only able to reproduce it once I removed WinSCP.ini, which seems to store something that made it connect regardless of BLOCK_SIZE set. (I wasn't motivated to figure out which part it was.) Anyway, v6 is looking good :)

I have added this request to the tracker:
Issue 2129 – Clear environment variables BLOCK_SIZE and LS_BLOCK_SIZE

I'm sending you an email with a development version of WinSCP to the address you have used to register on this forum.

Thanks I'll look at this.

More information on BLOCK_SIZE at https://www.gnu.org/software/coreutils/manual/html_node/Block-size.html
It would be advisable to also reset LS_BLOCK_SIZE

Logging in via SCP failed with "Unexpected directory listing line". Output showed that file sizes where shown in human-readable format (e.g., 12K). Indeed, my bash .profile had this line:

Commenting out this line fixed the problem.

This could be fixed by WinSCP unsetting $BLOCK_SIZE on login, maybe as part of the aliases and/or national variables. This would be a great addition.