Failed sync (error "connect EACCES"); how to solve?

Hello all,
I'm succesfully using Joplin on at elast 3 desktops and 1 android device syncing with webdav on my qnap succesfully (8 GBs data).
But this morning, I get this error syncing on a windows 10 pc:
Last error: FetchError: request to failed, reason: connect EACCES

Can it be a temporary error?
Or have I to do something to solve this problem?

I just discovered that the cause is Windows Firewall Control.
Worked fine until few days ago.
I already added Joplin to the allowed applications to connect is/out, but it doesn't work.
To make joplin connect to the web I need to entirely disable firewall.
Still investigating.
Not a Joplin problem, after all.

I managed to make the firewall work. It was a firewall update, causing the problem. I deleted all joplin firewall rules from the application (WFC) and now all is working.