@volcik I'm pretty much sure your problem is related to the mentioned(in #641) TCP port being used or in some other way unusable. In the PR mentioned above, I added some more logging and another flag to bind to the TCP port which should better suit our use case here.
If you want to try, I put binaries with the above changes on https://download.geany.org/snapshots/geany_win32_issue_641.zip (just copy geany.exe libgeany-0.dll from archive to your bin/ folder in your Geany installation and restart Geany). You should find some error messages at the top of Help->Debug Messages if there are errors.