Hi,
I can give few ideas, hoping they are not wasting your time, because never had this LSP thingy, so i only can guess.
1) Try to run LSP server inside a debugger, a real debugger like
https://x64dbg.com/ , looking for exceptions silently discarded and/or not logged.
2) Use
http://www.rohitab.com/ (yes currently on http only for some reason), this powerful tool need some get to know first, but i think you are gonna love it, anyway use it to track threading functions and event functions, also might help to track files, this monitor have great filter with great view for
API parameters and their result.
3) May be should be (1), compare the logging with working log, try to burn brain calories imaging what is going with great and famous LSP.
Hope that helps or give you thoughts.