Email loop detected error is completely unrelated to the topic at hand. Email Loop means that you somehow have outgoing mail from your helpdesk (most likely alerts) being sent to a system email and are being fetched back into the system which creates an endless loop of tickets being created, the alerts being sent to a system email, which gets fetched into the system and creates more tickets and sends more alerts, etc. You will need to figure out what is causing the loop and rectify it manually. We have no debugging tools or anything to help on this case (other than the warnings in the system logs like your screenshot).
As for the issue at hand (Ticket Thread being broken) you will need to consult your webserver (Apache/IIS) error logs, PHP error logs, MySQL/MariaDB error logs, and Browser Console logs to see if there are any related errors. (my bet would be the PHP error logs or Webserver error logs)