Default [Q] Movies app not generating thumbnail

The HD videos in my arc are directly downloaded from youtube, meaning it had a profile of Main@L3.1
The thumbnails in Gallery are generated when I was still on rom X-Gamer+GB lupusv2
I switched to UHD+Lupusv16, movie thumbnails wont generate in both Album and Movies app, neither in Gallery2
Tried rush kernel, not working.

My workaround is to change video profile to Baseline for thumbnails to generate, but it doesnt copy the original stream size(e.g. 95% but output is 90)
Some users here might want to use Movies app but thumbnails doesnt work, try using a media encoder and change profile to baseline VBR 2-pass.

Is thumbnail generation a kernel or a rom problem?
Other workarounds other than changing roms?