Hi 
No, I didn't switch from one sync target to another, I just:
Installed the Synology WebDAV server on my NAS and activated the 2 HTTP and HTTPS lines:
Created a joplin shared folder at the root of the NAS, I left the recycle bin enabled (default), but I wonder if it's useful and/or if it could cause problems?
The recycle bin in Explorer:
Set the timing to Joplin like this:
I still have a doubt about the path ending /, I wonder if I should put it or not, or whatever?
and I haven't touched anything in the advanced options:
Does everything I've done look correct?
I validated with OK, and that's when I said to myself that it might be good to make a backup. But as a reminder, the automatic save was causing me slowness: Slowness and sometimes “the window is not responding” error message, I then deactivated it.
So I just launched a manual backup via the Tools menu: Create Backup.
This is where I thought I would wait for the save to finish before starting the sync, but I didn't think that the automatic sync would start..., while the backup is in progress...
This morning, I had the message Backup completed:
It will therefore have taken much longer than usual, probably because there was sync at the same time.
Concerning the sync, it displayed more than 20,000 remote objects created then, the time of writing this message, the number went down again:
Then, the sync has just ended:
But as soon as automatic sync restarts, it displays remote objects created, even if I didn't make any changes, strange no?:
EDIT: a few hours later, the sync is still in progress, even though Joplin told me it was finished:
So, Joplin told me the synchro was over but apparently not 
I displayed the console, and here are a few lines:
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/import-enex-md-gen.js.map: Unexpected end of JSON input
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/index.cjs.map: Unexpected end of JSON input
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/markdown.js.map: Unexpected end of JSON input
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/ResourceScreen.js.map: Unexpected end of JSON input
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/Navigator.js.map: Unexpected end of JSON input
DevTools failed to load source map: Could not load content for file:///C:/Users/nonob/AppData/Local/Programs/Joplin/resources/app.asar/WelcomeUtils.js.map: Unexpected end of JSON input
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:03: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local eb976030d83c1a87fd0afe1cc7eddf12)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:05: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local e4a9c956c014a84251bf93c3f57b4dea)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:07: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local e201cdf8be861367a5e3f2e87f075ada)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:09: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local d527e6cb9773aaaaeb5546f0f7150113)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:11: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local c8a041b93dece189ae3d5f9b20fdaf49)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:14: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local c856dcd0e41f79838d468d02ca9493a6)
C:\Users\nonob\AppData\Local\Programs\Joplin\resources\app.asar\node_modules\@joplin\utils\dist\Logger.js:221 09:21:18: Synchronizer: Sync: createRemote: remote does not exist, and local is new and has never been synced: Resource: (Local bc16ef8b05c84ce6956c3d3f1204babb)
What do you think?
I also find that I can't use Joplin during syncs, it becomes too slow, maybe it's the same problem as during backups 
Thanks