2020-07-16 16:40:29.111 T:1390015360 DEBUG: COMXVideo::Open - decoder_component(0x0x5d414ba8), input_port(0x82), output_port(0x83) hdmiclocksync 1
vs.
Do not "sync playback to display" as that will force everything to be resampled and ARM devices are rubbish at that.
hdmiclocksync is "Adjust display refresh rate to match video", not "sync playback to display".
Are you sure you have both options, not just "sync playback to display"?
My point is that both options could be same. I don't think that a display refresh rate can vary all the time, so "hdmiclocksync" probably means "sync playback to display", not vice versa.
If so, it could be a bug. Maybe the corresponding GUI setting has been overwritten by a wrong compiler flag. When "sync playback to display" is always active, it can result in frame drops.
PS: I have been informed the devs. Stay cool. 
I just had a short dev conversation. We need a complete kodi.log (link, like you did before, log level 2). Thanks!
PS: Use local media for testing. Streaming has some additional unknown factors.
