Reposing this since original post was inactive and closed.
I am using SyncTrazor + syncthing v1.27.12 on windows and it appears to be a bug that happens randomly, perhaps due to some bug with “local addition” recordkeeping.
I am not sure if this is specific to OS or other environment but it looks like some bug that happens randomly and causes failure to add proper local deletion record to “local addition”, therefore syncthing keeps trying to re-download the same deleted file.
The behavoir was explained in the old post, but my experience is that after retrying deleting the files many times, there is some chance that the syncthing stops re-downloading that file.
Also the problem only applies to recent files. There were many earlier files I deleted locally and still exist remotely, but were never re-downloaded like recently deleted files. My guess is that older “local addition” entries are fine and only recent entries are affeted by this random bug that leads to re-downloading.
I first tried restarting syncthing but problem persisted. However, restarting explorer.exe seemed to have fixed the problem (or at least improved a lot). The folder has watcher enabled but I an not sure if that could be where the problem is. (Actually perhaps I should disable watcher for it since it is receive-only)
Have you been moving or renaming the folders in question by any chance? There is a bug with the watcher, i.e. if you enable it for a specific folder, then move the folder to a different place on the disk, and create a new folder in the previous path, then the watcher will still follow the moved folder, not the new one. This is until you restart Syncthing, which will make the watcher follow the proper path again.
And yes, the watcher is unnecessary for Receive Only folders. The only reason you may want to keep in enabled is to be able to quickly detect unintended local changes. Otherwise, they will only be detected on a rescan.
I didn’t do anything to the folder. It just re-downloaded deleted files all of a sudden (there may be automatic syncthing updates in the background, but otherwise I cannot think of any change or restart). I cannot say it is necessary the problem from watcher, but the watcher is one of the thing that is in the middle between filesystem change and “local addition” records.
My plan is to disable watcher and see if the problem would ever happen again, though the problem itself looks rare enough even with water on.