Hopefully this comment helps some folks: A week or so ago I removed Plex App from my Firestick 4k, and installed a beta version “kepler-armv7a-googlePlay-stdExo-7.30.0.16311-29f7de79.apk”, from Release Announcements - Android TV beta, using ‘Easy Fire Tools’ from the Google Play Store.
All the issues I was having (related to this thread) were resolved. Last night, I decided to go back to the public version to see if things were fixed. The issues started again. So, in response to @DaveBinM, I think the issue was fixed in beta, but not yet pushed out (like you stated).