Why does an error occur on Exchange server 2013 Imap Command error 12?

Question

IMAP

Good afternoon!
Recently, our *nixoids persuaded me to enable IMAP support on Exchange server 2013 CU2, to use not the Outlook client and not the web interface. After 2-3 weeks after switching on, we decided to upgrade the Exchange server to CU10. The update went well (there are no errors in the update log), the enterprise has 3 MBX servers (DAG) + 2 CAS (windows NLB). Connection from outside and inside is normal, with the following parameters: mail.adatum.com, 143, normal password, STARTTLS, outgoing mail - mail.adatum.com, 587, normal password, STARTTLS. The certificate for Exchange is issued by a wildcard to *.adatum.com, the certificate is assigned to IIS, SMTP services. When trying to delete a message using Delete, the following error appears: "Current operation on Inbox failed. The mail server for the [email protected] account responded: Command Error. 12."https://testconnectivity.microsoft.com/ passes. What could be the problem, can anyone come across?