Slowed down image if i activate subtitles on Apple TV

With a particular chapter of a tv show I am having problems activating subtitles as the picture frequently slows down, if I deactivate them there is no problem. In the Apple TV Plex app it works without problems. I have an Apple TV 4k 1st gen and the video in question is no big deal either. I have also tried with external subtitles and the problem persists. The rest of the tv show has the same format and doesn’t have this problem, so it seems pretty weird to me. I have also tried starting the video from the beginning, uninstalling infuse and reinstalling it, but the problem is still there and, as I say, in the Plex app it works without problems.

* Duration 57:42
* Bitrate 3521 kbps
* Width 1920
* Height 1080
* Aspect Ratio 1.78
* Video Resolution 1080p
* Container MKV
* Video Frame Rate 24p
* Video Profile main 10
* Codec HEVC
* Bitrate 3521 kbps
* Bit Depth 10
* Chroma Location left
* Chroma Subsampling 4:2:0
* Coded Height 1088
* Coded Width 1920
* Color Primaries bt2020
* Color Range tv
* Color Space bt2020nc
* Color Trc smpte2084
* Frame Rate 24 fps
* Height 1080
* Nivel 4.0
* Perfil main 10
* Ref Frames 1
* Width 1920
* Display Title 1080p HDR10 (HEVC Main 10)
* Extended Display Title 1080p HDR10 (HEVC Main 10)

I just tried another series with forced subtitles and when they load it slows down the picture, the rest of the episode works fine except when it goes to load the subtitles for a sign or something. It doesn’t happen in the Plex app. Is this an issue with the first generation Apple TV?