VKB-SIM

What would cause the jet to to wag or fishtail when I pitch and roll to a point where I loose control?
https://youtu.be/wC_6zRPW-xo

Towards the end of loose control
https://youtu.be/SMASpnfL4mk

I suggest Avia-H cams and 2 x #30s springs per cam, following this guide. And more training

looks to me like something funky is happening with the rudder. What controls are you using? You might consider going into the VKB joy tester program, and see what the axes are doing.