I have the same problem after updating dovecot 2.3.21, I am receiving the errors below for the accounts when I perform backups.
doveadm(user@user.com.br): Error: Purging namespace '' failed: BUG: Unknown internal error Error: failed sync dir: doveadm(user2@user2.com.br): Warning: mdbox /data/data/mailboxbackup/20240207/user2.com.br/u/ser/user2.com.br/mdbox/storage: Inconsistency in map index (42,40 != 42,56) doveadm(user2@user2.com.br): Warning: fscking index file /data/data/mailboxbackup/20240207/user2.com.br/u/ser/user2/mdbox/storage/dovecot.map.index doveadm(user2@user2.com.br): Warning: mdbox /data/data/mailboxbackup/20240207/user2.com.br/u/ser/user2.com.br/mdbox/storage: rebuilding indexes doveadm(user2@user2.com.br): Warning: Transaction log file /data/data/mailboxbackup/20240207/user2.com.br/u/ser/user2/mdbox/storage/dovecot.map.index.log was locked for 284 seconds (mdbox storage rebuild) doveadm(user2@user2.com.br): Error: Purging namespace '' failed: BUG: Unknown internal error
As in the case of our friend the other day, the error no longer happens on the same account, it happens on another random one.