I am getting an error message - Compass data missing - and cannot find the problem. I have checked all the connections but have not reset the computer or purchased a new PCB board. The compass is the standard RFC35 that was installed with the AP20. I really do not want to try the reset unless it is absolutely necessary. Or purchase a new PCB board until I am certain it will fix the problem.
I have the same equipment as you have, except I have the RFC35R rate compass. I never had lost compass data.
Perhaps you can open the compass housing and have a look inside at the board and the connections. Perhaps the compass in dead; try to find out if it provides a signal. If you checked all connections, did you measure integrity of the cabling? I cable may have been squeezed somehow. If you connect a core wire to the ground mantle on one end of the cable, you can measure conductivity between the core wire and the ground mantle on the other end with a multimeter. I find Simrad / Robertson quite reliable and robust.
I would agree with Michel. Assume that the problem is with the compass and not the computer. This is one of the reasons that I carry a spare compass (or two).