Well...
this morning, I did a major PC cleanup run, because I'm going to install NativeInstruments Komplete 8, and I needed more free space on the system partition.
So, I uninstalled some stuff and deleted some more stuff.
After I'd finished, I did a reboot, and guess what: the frequency display came back!
I did some more restarts, and yes, it is now working as expected.
What is this - some race condition on system startup?
The stuff I uninstalled was games, 3D demos and the likes, mostly stuff one would think does not change anything regarding Windows startup.
The two things that stick out though: I applied a small Acronis TrueImage hotfix (though, for some seemingly unrelated bug), and I uninstalled Oracle's Virtualbox.
Could one of those be responsible for the changed behaviour of CoreTemp autostart? (as both of those start services on system startup)
Anyway, case closed for me, for now at least.
