Anki - Next card review in <-36.2 years?
Solution: Date &amp; time were incorrect on the phone when I was studying decks in AnkiDroid. After syncing to the correct time - AnkiDroid thought I've been studying a set of decks for years, not minutes.

Therefore, make sure your time is correctly set and preferably doesn't change to an incorrect value, otherwise don't use AnkiDroid when your date and time are wrong. Set correct date and time first.