> Are you see sessions not being flacky while working directly with
> your backend?

Correct. I've tested backend standalone and this doesn't happen. Notice, that in requests above connect.sid is changing every request. That is not supposed to happen - with standalone backend connect.sid value is constant across requests and changes either when user re-logins or it expires.

Can it be because nginx talks HTTP/1.0 to backend?.. Ugh.