This statement in documentation makes me think I may be doing something wrong:
ref - https://winscp.net/eng/docs/library_session
"The class is locked against concurrent accesses from multiple threads. Though you can use several instances of the class in parallel, even from different threads."
So, I thought that I may be hitting some contention there. I will try to reproduce in small project.
I'd appreciate, if you suggest better wording (obviously, I'm not a native English speaker).