kodi cpu cycling and video intermittent

[bcsrepo]

i'm seeing an odd problem on my install, running as a service:

ExecStart=/usr/bin/x11docker --xorg --wm=NONE --vt=5 --pulseaudio --gpu --clipboard --homedir /home/htpc/kodi -- -v /home/media:/media:ro -- erichough/kodi

playing regular video from files plays for 8 seconds and then freezes, but never restarts. network traffic is low.

live OTA TV plays for 8 seconds and then pauses for 10-12 in a very regular cycle. the CPU of kodi.bin cycles simultaneously from <5% to 100%+ (of 400% for 4 cores), but the surprising thing is that it's when the CPU is high that the video plays, and when it's low the video stops. the cpu goes up and video works for 8 seconds, then the cpu goes down to idle and the video stops (with the '100' buffering progress showing) for 10-12 seconds.

(the tvheadend install is working fine, as i can simultaneously play uninterrupted video from that same channel on the live tv viewer on a remote machine on port 9981.)

any ideas as to where to start?

ubuntu 20.04.1 LTS
docker 20.10.5, build 55c4c88
kodi 19.0.0 (erichough/kodi latest)
tvheadend 4.3-1940~gfe0e5f1f9 HTSP v35
GPU mesa DRI intel hd 4600
i5 4 core

[bcsrepo]

For illustration, here's the CPU cycling during OTA TV: