I wonder why nobody has reported this issue yet
I can't really remember was it the same on earlier builds or not, but all latest Krypton-based builds have this problem: unsystematic Youtube video stuttering (frame skips), although Kodi detects source's FPS correctly and adjusts screen mode accordingly. Also strange that skip/drop counters stay unchanged.
Build:
Tested on several Kypton-based builds, including latest 8.1.4
Devices & DTBs:
K2 Pro (S905 2/16GB) - gxbb_p200_k2_pro.dtb
K1 Plus (S905 1/8GB) - gxbb_p200_k1_plus.dtb
Coowell V5 (S905X 1/8GB) - gxl_p212_1g.dtb
How to reproduce:
The best way to reproduce the bug - using of FPS testing videos posted below. Just look attentively a while (1-2 minute), and you'll defenetly see it. To ensure that is not a problem of testing videos themselves, you could watch it on any other device with automatic framerate switching (i've used Dune player and TV's internal client).
Sample:
I've uploaded testing videos, so everyone can reproduce the problem. But be patient, it may take some time for the glitch first appearance (1-2 minute or so).
Support logs:
K2 Pro logs. Just in case: the most noticeable glitches was at ~ 16, 58, 73 and 133 sec. of the video.