The reason for this issue is to be identified using more debug prints in the logs. Please follow the below steps to collect debug logs.
1. Login to Application and Navigate to Mail server settings (Incoming tab). Follow steps 2&3 if not done already.
2. Enable "Enable Email Debug" option.
3. Save the settings (If schedule gets stopped, start the schedule again from UI)
4. Download the attached 13012_8544269.fjar file.
5. Apply the fjar file.
Click here to know the steps.
6. Once applied, recreate the issue and share us the logs. If the size of the log file is huge, you can zip us the logs folder and send it to us using our FTP link
https://bonitas2.zohocorp.com/. Select the product as "ServiceDesk Plus" and ticket number as 8544269.
7. Kindly share us the subject and time of the mail to