Generally speaking you do not want to use the Plex web client for playback. It’s fine in a pinch and for certain video formats but if you’re playing any high end video or video/audio that is not natively compatible to the web browser, you’re going to see these sort of issues because your Plex media server is trying to transcode into a compatible version for the web browser.
Start by downloading a desktop app or the Plex media player app on your laptops and see where those are working well and report back in situations where they are not. In situations that are not working will you need to post more details about the video itself, the app settings, and the app versions.
