First of all, is Syncthing working in your main profile, or are you experiencing the same issue in all profiles? Basically, what should happen is when you install the app and launch it for the first time, a new device ID is generated, and you cannot change it unless you clear the app data and start from scratch (or you’ve got root access and delete the key files, but that’s yet another story 
).
In other words, I would make sure that Syncthing is up and running in the main profile first, and only then try to install and run it in other profiles as well. Also, I think there are some restrictions in the OS about what can run in other profiles at the same time, so I’m not sure if running Syncthing simultaneously like that is actually possible.