Picture in Picture disappears from episode to episode

Platforms iPhone & iPad
1

I’ve noticed that different episodes of the same series have different PiP options.

One episode will allow me to select PiP whilst the next, the icon won’t be present.

The series are all MKV H.264 files being watched on iOS 18x.

Any ideas why this might be happening?

2

I assumed it was the latest version that screwed this up for me but maybe not as I’m having the same problem. Was working fine and now it never shows.