This is known issue people are experience with CM9, Gummy, and AOKP. MotoBlur + Android 4.0.4 is based of AOKP inheriting its issues. Usually a restart or two fixes the issue, but it is somewhat random. I believe the issue involves bluetooth but I guess no one really knows. I heard toggling bluetooth sometimes fixes it as well.
However you say it doesn't even ring, I have never had it not ring. But have experienced the rest.
Samsung Galaxy S4 16GB (VZW), Gummy 2.1 (4.4.2) modified and built from source, TWRP 220.127.116.11 Touch Recovery, SanDisk Class10 64GB ExtSD
Moto Droid 3 - Gummy ICS 4.0.4 Modified Build 1.2.x built from source (retired)
Moto Droid 1 - ChevyNo1 SS 5.6 1.0Ghz LV Kernel (retired)