Today I learned that Mojave has a 31 character password limit.
In general I like long random passwords managed in a password manager.
However, there are a few passwords that I find I have to type frequently. The password to access the password manager itself. The single sign-on paasword. These I like to be long passwords easy to remember and type but difficult to brute force.
While the single sign-on system at issue generally supports a longer maximum password length, it turns out using a length longer than 31 characters is a way to lock myself out of my Mac. Trimming the password down to 31 characters fixed it.
Mostly leaving this post as a note to myself for next time.