KII Plus livetv lags/audio loss

running 9.2.2 on KII Plus.
I occasionally have stutters/lags with audio/video while playing DVB-T channels (didn’t try DVB-S yet), either SD or HD ones from local tvheadend 4.2 service. These stutters kick in at least after some hours of livetv streaming and least until I reboot the device:

I have this issue with hardware demux with CPU temp staying aroung ~58C. Is this enough to trigger CPU throttling?

Is this a common issue and is there something I could try?

Other issue: video playback completely freezes for some seconds every few minutes. This apparently starts to happen after a few hours of livetv playback:
tvheadend log
kodi log

Please note this line: codec:vdec1 video changed to 3840 x 2160 60 fps clk->667MHZ
It is apparently telling that video changed to 4K resolution. Don’t know if it is actually relevant but I have only 1920x1080i @50hz in whitelist and channel source is FHD.