x265 = 3.5+37+12-4e46995bc-.Mod-by-Patman.-x64-msvc1931

I'm encoding a video that was previously trimmed in another application. I set preset Fast. in the resulting video, a one-second freeze occurs at the beginning. this only happens in Pot Player. VLC doesn't have that. Light Alloy has it, but it can be removed with the hardware color settings. Tried to set different video settings in Pot Player, it does not affect in any way.

If I turn on B-Adapt in the encoder settings, then there is no such frieze anymore.

Why is this happening? What a small detail, but it could spoil the video so much, it's terrible.