Hi,
It seems that your issue is coming from the text content of your delivery.
First, just delete the text content and try to send a proof...
Check that there s no issue
Second, add all static part of the text content and send a proof
Check that there s no issue
Add first dynamic element to your text content and send a proof
check that there s no issue
Continue like this until you'll be able to target the dynamic element of your text content that create the issue