You say that your PBX lost registration with your sip provider too, but they didn’t see that happen? That’s a little weird. I don’t believe that losing connection with your sip provider would cause your pbx to also lose connection to your phones. And your server clearly did lose connection with the phones. Is your server local, or is it hosted?
If it’s hosted, I think it’s likely that you had some internet connectivity problems. We are dealing with a similar issue, and after tons of troubleshooting, it came down to unstable internet. If this issue keeps coming up, download ping plotter and see if the drops in service correlate to when your extensions go down.
But those other errors are interesting too. Maybe it’s a DNS problem. I don’t know much about that, so someone else may need to chime in.
Also, what ISP do you use? I’m just curious.