The current Fastpass+ system has presented ways for guests to take advantage of the existing infrastructure in the park. One "loophole" allows guests to use park tickets and/or Magic Bands of guests that have not entered the park on a given day. This loophole (dubbed "In-Park-Validation") allows guests to reserve more than the 3 advanced booking Fastpasses by utilizing multiple IDs.
Beginning June 7, 2017 Disney will attempt to close this loophole by requiring all tickets used at a Fastpass+ entry point to be validated as a ticket that was used to enter the park that day. A similar enforcement is currently in place at Disneyland at the paper Fastpass kiosks. It is unknown at this time if any penalties will be accessed for guests attempting to continue to use this loophole, but a suggested penalty would be a "lock" of the guests My Disney Experience account for excessive abuse. Such a "lock" would likely be able to be fixed at Guest Relations.
The valid theme park admission associated with your Site/App account and used to make FastPass+ selections must be the same valid theme park admission that you will use for entry into the park on the day the FastPass+ selections are redeemed.
This reportedly comes after third party "tour guides" have been abusing the previous system with extra Magic Bands that are not linked to a My Disney Experience account. These tour guides would make Fastpass+ reservations at the kiosks to be used for guests that hired them as "guides".
Accounts may be locked if a guest has redeemed a Fastpass+ selection on a ticket that was not used to enter the park on a particular day. Accounts can typically be unlocked at guest relations.