I have an OSMC Vero4k. It was running Kodi 17.x and last month it did an automatic update to 18.1 and recently I believe to 18.2.
Before and after the update to Kodi 18.1 I was running the official Plex app, version 0.1.6.
As Plex was having the issues described before, I followed the advice of uninstalling 0.1.6 and then installing version 0.1.7a2, downloaded from here: https://github.com/pannal/plex-for-kodi/tree/develop
However, the issues mostly remain.
Edit: I completely reinstalled Kodi on the Vero, and re-installed Plex 0.1.6. No change.