So, here we are… Day three & it hasn’t moved…
I ran the last update. Then I noticed that some of my sleeve art was getting messed up (which I posted about) but I couldn’t be 100% sure that the sleeve art problem wasn’t there prior to the update, so I removed the two box sets that seemed to be involved in the muddle, with the intention of clearing the caches & re-adding them to see if it solved the problem.
But Roon constantly had the little purple circle spinning. I figured it was doing its scanning/analyzing thing & decided to leave it for a while. When my patience ran out and I finally clicked on the circle to see what it was doing, I saw that I was back in “applying changes” hell.
Of course, it means that I can’t play any music, because it would be reading from & writing to the hard drive. So I’ll just consider my Roon payment a charitable donation for the time being. 
The question, as always, is what’s it doing?
No one knows. It’s a mystery.
Secondary question which has also remained resolutely unanswered by anyone at Roon…
How is this different to my daily back-up?
I gather it’s slow because my collection is so big. That makes sense.
I’ve also been told it shouldn’t do any harm to just restart Roon & force it to abandon the process. Which, for one reason or another, is what I’ve always had to do in the past.
But I can’t help thinking that if Roon is going to keep on trying to do this & bring my digital life to a virtual standstill periodically, I should let the process finish & maybe… Just maybe… It’ll go away & leave me alone.