Video flicker on QNAP fw update

Hi, I posted this in the QNAP forum, where I thought it belonged, but I was told to post it here instead, so here goes:

Since upgrading QNAP fw to 4.3, and Plex to 1.7.3.3937, I have large jittery horizontal bands on all videos. I’ve done all kinds of control tests; switching HDMI cables, plugging the NAS directly to the TV…I haven’t changed any settings on Plex or on my Yamaha amp. These bands do not appear when watching videos on QNAP’s baked in Video Station Player on HybridDesk Station, nor on Plex Player on my laptop.
It’s clearly isolated to Plex on HybridDesk Station. I have since installed two 3rd party players, MyKodi and Plex Media Player 1.3.4 for HD_Station 3.1, both from “Father Mande,” and the videos play flawlessly.
I have also tried (I think!) every possible combination of audio out settings, like disabling DTS, etc, to no avail.

Any help MUCH appreciated!!