Hi there!
Currently I'm running Ubuntu MATE 16.04. Sometimes when I try to connect to Steam for Linux it asks for the steam guard key. After entering it says "Steam is having trouble connecting to the Steam servers."

Some hours ago it was all fine. Now it shows the warning message everytime, sometimes asking for steam guard code (and the key pops up on my phone) and mostly it just showed the warning.

I tried to reinstall and purge everything of steam on my machine. I had no installation issues and all libs are installed. My router had a restart and has no problems at all, Steam is the only platform with a warning or error message, everything else works like a charm.

If I run Steam on Wine it runs well and the login is possible.
So my question is, what could it be?

Thanks for any helpful answers!