I’m running syncthing on my home Synology NAS with some Send Only folders with a Raspberry Pi backup machine that has corresponding Receive Only folders. In the “software” folder the receiver says that there’s a local addition, which is the directory “macOS/OBS”. However this folder is present on the sender so it ought to be there. On the sender it contains 3 files and on the receiver it only contains one file. If I select “Revert Local Changes” on the receiver then it does a rescan and just goes back to the same state as before with that same folder showing up as a local addition.
Something looks wrong/corrupted, because with no ignore patterns in place, the two folders should have identical global and local states, but they differ. I would try to remove and re-add the folder in Syncthing on the Receive Only side, and let Syncthing rescan it.
Also, with Synology in place, please make sure to enable “Ignore Permissions” in the Advanced tab in the folder settings on both sides.