Some videos don't start

Hello,

I just bought a 4k select Fire TV stick and some of my local network videos are not playing (plex server says it is but on the tv it’s stuck at 0 seconds with no image and sound)

All my videos are H264/AAC 1080p.

When it works plex server transcodes the video (H264 to H264 ???).

My previous (very old) Fire TV played those movies (direct play) with no issue but instability and os freezes.

What can I do please ?

Get a different Firestick.