I’ll guess this is an issue with a few media files, they way they were encoded.
To help you get started around here, the support articles are the user manual.
The forum help is great, but being a technical exercise, requires attention to detail.
For your issue, the mediainfo from a couple of problem files and a sample file will help a lot.
Include an exact description of your hardware, software, and network.
This all gives people a roadmap to reproduce the issue.
When you get some time, zip and attach your server log and your player log.
That’s a lot of work for any of us, but in the end you’re Happy Plexing
okay good luck!