I tried to move one test project to server. B4A 8.50, targetSDKVersion = 26, uses JavaObject (and , of course, Core).
I logged as administrator on local PC and server.
I tried two variants: to open using assigned to shared folder letter and using UNC path. Both works fine.
One thought ... Take a look x.b4a in Notepad. Maybe something strange in ModuleX lines ?
When you want to add existing module, B4A offers - "copy to folder", "relative link", "absolute path".