Hi all,
I was having the same issue and I believe that it’s because I changed my user password in admin panel and did not update the android app login. I was having repeatedly failed login attempts.
I was able to get rid of the error message by deleting the content of the table "oc_bruteforce_attempts " on nextcloud database.
DELETE FROM nextcloud.oc_bruteforce_attempts
You can put a where clause and limit it by IP so that only your login attempts are deleted:
DELETE FROM nextcloud.oc_bruteforce_attempts WHERE ip ="X.X.X.X";