When you check in to your resort make sure everyone is linked and MBs active before heading to the parks. We had added a grandparent after booking a free dining package and we always check that our bands are ok at the front desk before heading to the parks. It took them 2 hours outside Epcot to fix the issue and allow us to enter (missed 2 of our 3 FP+ no recovery given; CM dismissively said you have 2 extra magic hours). Park was about to close and we rushed to the food booths to get something to eat.
We were assured the issue was resolved and we were held again on
MNSSHP 2 days later (we had been to another park and so park tickets were fixed but not special event) for 1.5 hr despite showing the credit card purchase and the grandparent on
MDE (and I had FP+ setup for them as well). So if you add people to a package and maybe if there is a free dining offer I believe they flag your account and IT has to clear it.
Budget extra time, make sure they fixed special event tickets as well; be prepared with snacks and water.
It left such a bad impression that said grandparent never joined us again.