Both the open loop and close loop end mirror TF look fine to me. There is no oscillation at 0.3 Hz.  Note that striptool used EPIC channels are sampled at 64 Hz, so the oscillation could be an artifact (down-coversion of higher frequency noise?) You can double-check with dataviewer.

From the movie of the transmitted beam it is not clear the frequncy of the oscillation but it likely to be from a steering mirror (BS or PR). It would be useful to take a spectrum of their motion.