Accounts of some Reddit users have been locked out or suspended due to irregular behavior that could suggest unauthorized access. Reddit security team has stated that they plan on allowing affected users to perform a password reset in a few hours time. The suspected cause for the unusual activity seen from the locked accounts is a credential stuffing attack, which takes advantage of users practice of reusing the same login password for multiple websites and online services. Users with an email address associated to the Reddit account should receive a notification to reset their password.
Source: https://www.bleepingcomputer.com/news/security/reddit-users-locked-out-of-their-accounts-for-unusual-activity/