Big pitch oscilations, when gps signal is jammed on a plane

Hello, I live in a country with a lot of gps jammers are nearby big citties. Recently I found, that on my plane when gps jamming is present horrible pitch oscilations start, they are defenitely related to gps jaming, not pids, because plane flies OK, when gps signal is not interrupted. Also this is not a servo issue, because it stops oscilating in manual mode. You can see the exact behaviour in the link to youtube video. It is not a single case, it happened to me many times. These three videos show variations of the behaviour.