really odd problem with SSH/SFTP

[planetinse]

I've been using SSH/SFTP for years on the LAN side with pfsense
usually with the Bitwise client from a windows box (on the LAN side)

Recently did a big networking reorg and also moved from 23.04 to 2.7.2 and at first i had SSH problems - it disconnected as soon as i started to do stuff that required lot of updates (ie. like top)

after visiting here and other places i changed "Firewall Optimization Options" to Conservative - voila ! - SSH works perfectly now.

SFTP however - I CAN download large file(s) from remote host
but I can NOT upload large file(s) to same remote host .... getting "FlowSocketWriter: Error sending bytes" ... an existing connection was forcibly closed by the remote host.

I can use WGET on the host and download large files without issues.

total mystery to my limited brain......

need troubleshooting ideas, or things to try.