Error Code bizhub c3350 fax problems

I have a few c3350 machines that are having weird faxing problems. Phone line connections are correct, if I were to call the fax, a connection would be made both ways with dial tones etc.

However sometimes when the machine wakes up I notice faxes can not be received or send (would get message to check line connection). I would have to restart the machine to make it work again.

Any ideas how to trouble shoot this? Its pretty annoying because we have no idea when the fax is down or not until we try to send something or not receiving any faxes for a few days.