Hi @michael5, and welcome to the forum 
This may happend if you enter wrong password too many times. It locks the account for 10 minutes after 3 failed attempts, by default.
Unfortunately sudo does not inform user about that in any way.
If you like to change those settings edit /etc/security/faillock.conf file.
Take a look at Sudo/user stops working seemingly randomly - Support - Manjaro Linux Forum
Hope that helps.