I found a Bug, which breaks HW-decoding of TV-channels under CoreElec 9.2.2
(full discussion of the issue and logs/samples can be found here: https://discourse.coreelec.org/t/tvheadend-choppy/10574/23)
VERDICT >> FOUND the issue-maker: as soon as an EXTERNAL USB-GRABBER is activated in Hyperion.NG, the stutering / choppiness starts (fushicai utv001, not plugged in!).
==> Deactivating the external grabber instantly fixes the TV-channels not being decoded in hardware!
Now - to the solution ?