Reminder emails all fail

Reminder emails all fail

My invoice emails all work fine (the email is validated) but reminder emails allways fail and the only message I get back is :

"Your message to the following recipient was not delivered. Please find the details below.
Bounced Address : XXXXXXXXXXXXXXXX
Bounce Reason : uncategorized-bounce
Bounced Time : Nov 11, 2021 12:03 PM AEST"

Note I removed the customer email for obvious reasons.  It seems obvious that this is a bug but it has existed for some time and obviously is an issue that needs to be addressed ASAP.