This is Sitecore 9.1.1, and we're working with doing some test runs on user creation. Basically folks are creating users to log into the front end of the site, but they're sometimes not picking the right user profile in the user manager. So they go to delete the user, which works fine, but then they try to recreate the user immediately (same username) and get told the username is in progress. After an IIS restart, it seems to unlock this, so it almost seems like a cache is in effect.
From a custom standpoint, we did tie into the user:created, user:deleted, etc pipelines to update information in a custom database whenever a change was made. There's no check against that database to see if a username is there, so it should be cleared once done.
Is there any "lock" on usernames that occurs after deletion?