"The best business telephones in the world."

Here is what we got:

- VoIP by Telekom

- A Fritzbox 3490 being the PBX
- A Snom M325 running version 4.00 B0002 being the DECT system
    
Now it happens quite often that my handset is busy for incoming calls.

And it doesn't matter if it's an internal call from the VoIP client on my computer or an external call.

You either get a busy signal or when I call myself from my cellphone I get the announcement "not available at present".

Outgoing calls still work fine.

And everthing works fine again after simply turning the handset off and on again.

So what's wrong here?

And BTW using Firefox 58 the login for the base station asks for username and password twice.