The past few weeks, while playing HEVC files (mostly with ASS subtitles, remotely or locally) from a series in a .mkv container in Brave and other Chromium browsers, I keep getting the following playback error randomly(often at the first minutes of the video, sometimes in the middle):

The video is direct streaming (MKV to MP4 container conversion). These are the logs for when that happened once (pastebin). I have full log files from when this happened another time a few minutes earlier, if that’s needed.
Server Version#: 1.32.3.7192
Player Version#: 4.108.0
Some other new issue I’ve been encountering recently is a " Conversion failed. The transcoder exited due to an error ." message on the Plex TV app(client v5.62.0) of my LG TV with webOS 3.4 , just before the end of the episodes. It says that it is a transcoder error but the media is always direct playing. Sometimes this happens in the end of every episode, sometimes it doesn’t. Should I create a new topic for this?
I don’t know if it’s relevant, but something that I started doing recently is adding and removing some devices from the “List of IP addresses and networks that are allowed without auth”.