Interesting.
Meanwhile, I found some differencies between 8.99.2 and 9.0.1 regarding audio delay (I know, its a bit offtopic, but maybe it is also relevant to the same root cause).
Before, without AVR, audio delay 0 usually works, and was same for h264 files from network disc and internet streams (prima TV via plugin for example) for basic setup C2->TV with 2m HDMI cable. Actually, I vaguely remember, than even before in some nightly I setup -75, but I am 90% sure that with 8.99.2 it was 0.
With 9.0.1, for the files I need to setup -125 delay. Which would be fine, I get used to do initial audio delay setup when installing environment (it depends on length of cables, type of TV and AVR in the way). But now, setuped audio delay works for 264 files, it doesnt work for (some?) internet streams. For prima for example, I must revert delay back to 0. And this is very bad for user experience, cant do this to my old parents, they didnt understand OSD audio delay things…
I didnt remember that difference in previous versions, the same delay usually works for all videos. Cant test DVB-T2 TV unfortunatelly, due not sufficient shared home antenna channel parts (still ).
I could just guess it could be because lateframe fixes, which goes up and back, but it could be maybe also with something between Kodi 18 and Kodi 18.1 version. I didnt know that yet, but I planning test different lateframe patches back in time agains latest CE…
But I think your finding is also interesting and worth look into…