Desktop sync client connection lost

I am using newest client version 2.3.3. on Ubuntu Mate 16.04 LTS. Client works on my other Ubuntu computer, but for some reason the connection stopped recently on this one. Haven’t occurred before. Client displays something like this: No connection to Nextcloud in address (my address). Operation canceled.

(Also my mobile client has repeatedly pulled me on the log in menu, even if I fill my info correctly. Owncloud mobile client still works for my files though, but this issue is probably another story for another topic…)