Do want to help. Still do. The responses (or at least mine) was severely misunderstood. Agree that @AudriusButkevicius response makes no sense (rather serves no purpose), but at the same time the initial question was not concisely or clearly written and my similarly complicated response was misunderstood nor was it acted on to address the issue. But understand. The issue is tough and complicated to type out as was and is the likely solution. @AudriusButkevicius always responds very quickly and seems to want to help many users. All this being said, forget about those responses.
After everything is setup and working would recommend restarting to see if everything is still working. Assuming Syncthing stops working yet again after a restart done on purpose for problem solving one should then check the config.xml file in the Syncthing data location of the logged in user and see if the shared folders previously are still listed in the config.xml file. If they are not Syncthing is starting as another user or pulling/ using data from a different location than:
/Users/USER/AppData/Local/Syncthing
Additionally if the config.xml file in the above location does not have data in it about the shared folders even when everything is working this would indicate that Syncthing is using a different data folder location. This is why would check the config.xml file prior to restarting as well after everything is setup as desired. Be careful though. Since have setup Syncthing multiple times already you may see a config.xml file that looks like it is correct. Check the folders ID’s in the config.xml and make sure that it corresponds to the folder ID’s listed in the GUI to match up a config.xml file with a running instance.
A restart isn’t purely necessary to rule out Syncthing being run as a different user or using a different data location but it is a very clear, easy, and absolute way to ensure that the Syncthing task is completely stopped before restarting. One could alternatively to restarting kill the Syncthing task and restart Syncthing in the same way in which it would start after a restart before checking the config.xml file.
The reason to go through this task and check the config.xml file is to try to decipher where Syncthing is storing it’s data while it is running. If Syncthing starts either with a different user or with a different data location anything previously setup will not work and it would make very good sense that Syncthing would function like a brand new instance where everything can be re-added and re-indexed from scratch.