I have noticed a problem that my pc is not getting at every startup the same Identifier and therefore not syncing my Files.
After a restart of the PC the right Identifier comes up and everything works as usual.
How did you install Syncthing? What are you using to access the Web GUI?
I suspect that you may have two different installations and whichever one happens to be quicker at startup, wins the race for port 8384 where you find its GUI.
Or do the IDs change randomly, not only those two alternating?
I mean did you enter the URL in Chrome’s address bar, is there some shortcut you or the installer created? Are you clicking on the link in some console output?
Sorry I don’t know much about how the Windows installer works, but it should give you access to the console output of Syncthing somewhere. There you will find some info about ports and paths used.
There is also a path overview in the About dialog when you access the running instance in Chrome. Check whether that path somehow seems volatile or changes together with the ID.
Then you need to figure out where this wrong instance is started from. We can’t really help any further since this is an issue specific to your system / service setup. Anyway, whichever instance is started first hogs the TCP port 8384 on localhost to present its GUI. The other one may actually be running just as well, but it automatically sidesteps to a different GUI port. If you can find the logs / console output from that service, it will tell you where to reach the expected instance’s GUI.