This question may have been answered before but a quick search didn't reveal an applicable thread. Sorry If I missed it.
I didn't use my Pi-3 wth Volumio (pre- and latest version) for a month or two. Previously it worked perfectly with some network shares mounted on an up-to-date Synology DS215+ with SMB 2 and 3. Network-settings have not been changed.
After switching on all mounts stay disconnected whatever I try. I enabled all versions of SMB (1 to 3 and large MTU) on the NAS for troubleshooting. Preferably I would like to skip SMB 1 for security reasons.
Adding vers=1.0, vers=2.0, vers=2.1, vers=3.0 to the advanced options all fail with an error message that flashes quickly: Error adding networkstation (115): Operation now in progress. Please refer to bla bla.
Then I updated to the latest version (with Pi-4 support) and went through the same stages. Rebooted NAS several times. Problems only from Volumio not being able to connect to the mount points.
I tried mounting with a different user account (verified working from Windows and Android) but to no avail. I tried Searched for ages on Google and Bing, no solution, my Volumio, at least network mounting functionality has died on me...
Only means to play music now is adding a big USB-drive until I can fix the connection to my NAS. What I am missing is some 'Disconnect' or 'Reconnect' option in the mounting section, all you can do now is completely remove a mount or edit something first.