I was having this problem in 2.8.3 and I was hoping maybe it would fix itself when I upgraded to 2.9, but I did that and it is still happening.
When I create a new contract, A reminder should be created, and the contract manager added as an invitee to send out email notifications at the specified date, but that has not been happening. A reminder gets created but it has no invitees.
If anyone could suggest a fix for this I would be grateful.