Front to back wobble

When flying in loiter or Auto the copter tends to fly forward then rock back it wobbles front to back until I tell it to stop going forward. It’s pretty stable for the most part but the wobble is very strange.

Copter is a TBS discovery I have the CG pretty spot on per their instructions.

Log file is attached and an picture of the CG spot on the frame.

CG related.

So what was the problem/solution in the end?

I’m having a similar issue on my Discovery.