I had some problems with my KS as well, not this particular problem but I do understand your frustration. It took Plex a while but eventually they figured it out and now it’s working fine. I do believe them that now it’s something to do with Samsung because this problem seems limited to a very small subset of the KS series so it makes sense that something is different on these sets and unless you have one it’s impossible to replicate the problem and test.
I have Emby as a backup solution but not for my Samsungs because if you’re not in US, UK or Ireland you can’t get it. Goes to prove that no solution covers everything.
Unfortunately the only thing you can do is wait and bug @sLumpy from time to time for an update 
