It seemed unusual to me as well; and I dropped a comment much to that effect a few days ago.
@philm responded with:
Of course, being in Stable doesn’t mean it’s generally available to the masses, as your screenshot indicates.
Those who find it might be curious enough to try it.
The fact this kernel is being shown as “available” with the basic command is indeed a potential stumbling block. It should have been explicitly listed as “RC” or not at all.
Probably overthinking it here. 
Only advanced users (defined as those using the commandline for the sake of this comment) would likely find it. And others won’t see it anyway. For all we know at this point, that RC might even become the released version. 
Solved.
The problem seems to be related to the fact that I have an instance of ffplay on my desktop (watching my security camera). Stopping that while playing videos stops the hangs.
Putting this here in case someone comes up against a similar problem in the future.
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