All fingerprints erased This morning, I woke up, opened my MacBook Pro 2016 13" w/ TouchID, and all the fingerprints were erased. Nothing should have caused this, and nobody else knows the password to my account. How can I determine what caused this so I can fix it and avoid this in the future?

Running macOS Sierra 10.12.4 (16E195)

It did NOT update software or anything outside of the usual last night, it didn't even reboot.
I had a similar error with my MacBook Pro 2016 15".  You should be able to solve this issue by updating your software version to High Sierra (which fixed the issue on my computer) if possible.  Check in your console logs to see if your computer experienced a kernel panic, which may have caused the loss of your fingerprint data.