Custom Message in Proof

I've had some complaints by people who aren't getting the correct custom message when a proof is shared. We have some proofs that are shared with 10 people, and then those 10 people share with another 3 each, meaning the custom message is constantly changing. We've had examples where someone else's custom message appeared in the notification instead of the one they wrote, and also it seems that if you don't check the box for custom message, it will send with whatever the last message was instead of being blank. Any input on how these messages work? I am baffled and confused by every notification within Workfront, so trying to sort them out as I can. Thanks Jill Ackerman