Update (to 16.0.1) can't complete while platform is running. Platform can't be exited while updater is running. Oof.

So, I don't know why I didn't experience this on my flash drive, but it happened on my external hard drive. Not sure why.

I can't recall, but doesn't the Platform installer force the running Platform closed? It didn't do that and threw itself into a loop. Had to use Task Manager to quit (neither would allow me to).

No big deal, I just downloaded the new Platform installer manually. And, that worked perfectly.