Was having the same problem on Android tablet running 7.26, downgrading to 7.25.3.14365 fixed for me.
Also had the problem on Android TV (Nvidia Shield) running 7.26 and fixed that by disabling the “New Player” in settings (not an option on Android devices).
https://www.reddit.com/r/PleX/comments/eg4jwf/playback_has_stopped_because_connection_to_the/