Rear engine tach is not right

[frank.oconnor19]

I have taken a few flights lately and notice that both the rear engine tach and primary cht gauge are bouncing around. Looking at the attached video you will see that the manifold pressure is constant as is the fuel flow. No issue from a performance point of view. The prop sync does not seem to want to work either. Has anyone seen this? Ideas?

https://photos.app.goo.gl/Zwa22jZUmFTSw1gT7