soundpoint 650 with extension module rebooting

Hello all,

I have a customer with two SoundPoint 650 phones with extension modules attached. For about a month now, they have both been rebooting at random. It doesn't matter if they are on a call or not, low call volumes, high call volumes. etc.... There is no rhyme or reason that I can find to when they reboot. all the other phones in the office are working fine. The PoE switch has been replaced (twice) and the cabling from the switch to the wall plate has been tested and certified.

The phones are running firmware version 4.0.10

Has anyone come accross this before? I didn't see anything that fit my set up in the forum anywhere.

Thanks,

Chris