Resolution 4k, Kodi 17 doesn’t seem to play correctly full hd movie

hi guys ,

Strange problem for my htpc since I install GTX 1050 instead of my previous GT 650.
TV Panasonic 4k (DX750F) , windows 10 pro , latest drivers 376.48 , kodi 17 RC2
I witch my resolution to 4k (instead of 1080p with gt 620)

I ve no problem for a movie in 4k 50 or 60 hz.
But when I try to play a movie encoded full HD at 24 Hz (or 23.976) , the picture stutters a lot (even if my TV say it s 24h in 3840×2160)

any ideas ?

thank you veyr much