Library says "connection timeout" but ping host works

I get a connection timeout or no route to host error if I try to access my files that are stored on my NAS.

Same if I try to edit my sources in Library settings.

I tried to ping the server via ssh. No problems.

Could be a smb problem. How can I check that or renew the credentials?

ERROR: SMBDirectory->GetDirectory: Unable to open directory : 'smb://USERNAME:PASSWORD@nas/Media'

unix_err:'6e' error : 'Connection timed out'

If I add a new share and use the IP address instead, I get the credentials dialog box and that works

Reboot helps. But after 24 hours same problems again.