First, this has the makings of a very good application.
I have the application installed on a Windows 10 PC. It is sync’ing its data to a webdav service on a NAS.
I have the application installed on an tablet running Android 8.1.0. Over wifi it is connecting to the webdav service and sync’ing correctly.
The sync’ing is NOT working correctly on a smartphone running Android 9.0 (PIE). I tried both the webdav and nextcloud methods. I then set up the nas to share the webdav data as a file share. I tried fileshare sync’ing. It does not work. In the file share option you do not provide a means to set the username and password for the file share connection.
In all cases I am using the latest versions of Joplin. All of these work has been done in the last 2 days.
Google is accelerating the upgrades of Android phones to version 9 and 10. This problem needs to be fixed.
In researching this issue I see others have reported it and have done some investigation of it.