tcpdump confirms that with 2 mails in INBOX (1 relevant to the mail loop check, with agreed upon sender and subject, and 1 “legitimate” email with entirely different sender and subject)
the check_mail_loop fetches both emails and then proceeds to delete both of them instead of only the one it should care about.
This is a data loss bug introduced with werk #16043
AAHK0 CAPABILITY
AAHK1 LOGIN CMK-Mailloop "MySecretPassword"
AAHK2 SELECT INBOX
AAHK3 SEARCH NOT DELETED
AAHK4 FETCH 1 (RFC822)
AAHK5 FETCH 2 (RFC822)
AAHK6 STORE 1 +FLAGS (\Deleted)
AAHK7 STORE 2 +FLAGS (\Deleted)
AAHK8 EXPUNGE
AAHK9 CLOSE