You may find from time to time that the report emails are not coming through. This could be due to the task failing, or the emails are coming through, but they are either being blocked or they are falling into the junk/spam folder.
Firstly, to rule this out as a possible cause, could you please ask your customers to do the following:
Check their Junk/Spam folders.
It could also be due to the emails being stuck in Microsoft 365 Defender, and after being released from Quarantine, they will receive the task reports. Could you ask the customers affected to check with their Internal IT and ask them to check for any blocks by Microsoft 365 in Quarantine?
Once these have been checked, if your customers have confirmed that there is nothing in their junk/spam folders, and nothing is being blocked by Microsoft 365 in Quarantine, please get in touch with the Delta support team, confirming the above.
Could you also include the customer code, the reports they are not receiving, and the last time they received them. Once we have received this information, we will investigate further.