I have an Axxess v10 with a similar problem, only slightly more weird. The PRI is divided into two trunk groups at the CO. Several times, the channels on one trunk group will lock up, while the channels on the other are fine. Reset at the PBX or CO corrects the problem.

We’ve replaced the T1 cards in the PBX and smart jack. AT&T can’t find any problem, and there are no errors shown anywhere – the channels just lock up until the circuit is reset.