So you’re not gonna get it anymore ? Since you tested ng? 
You could always save tar from .update folder before rebooting.
Just a hint 
Just tested 19.5 nightly.
Problematic channel slowed down fo a sec but it never stopped like in 20 nightly. Can’t test any further as TV is occupied 
Some more testing:
Seems to play perfect with 19.5 nightly but had to turn off dhcp in coreelec settings and leave it on manual
Back with 20 nightly card and it play perfect as well 
what’s going on ?