I am seeing something similar. Previous Vero4K didnt do that and when I clicked to Play, it displayed picture almost instantly. And when I stop movie, it returned back to kodi almost instantly.
I just got Vero V, updated it to newest system and when I stop movie, there is like 4 seconds of black screen before it shows Kodi again. Refresh rate adjusting and similar settings are all off, I never used them. My video output is set to 60Hz, but it does it also at 23.976 and 59.94Hz setting. This happens only when stopping movie and returning back to Kodi. When I hit Play, it shows picture quick, like I am used to see.