Touch ID sensor is currently unavailable.

The error is intermittent for me (well, it was after restarting in the first set of troubleshooting steps) but I did not see the system prompt asking me to confirm using Touch ID as in the second set of steps.

This particular error has only appeared since the most recent update. However, in the past month or so, I have had to unlock both the main application and the Safari extension – even when I'd just unlocked the main app – which I don't believe was the case before.