First iMac Touch ID greyed out..... then removed itself from Preferences altogther

So, a week or so ago, I noticed that Touch ID was acting a bit strangely. It seems to happen occasionally and I didn't think much about it. Then, suddenly, it wouldn't work at all. If I looked at it in Preferences, all the options were greyed out. I tried pretty much everything people mentioned to try to no avail.

As of yesterday afternoon, Touch ID doesn't even appear in the Preferences window any longer. Charming!

Thoughts?

FYI - everything else seems to work fine, I can get in with Master Password, etc. No issues but once you get used to using Touch ID, it's tough to do without.