Hard to say, several people have said they have had multiple tickets in the DL app and not have any issues with Boarding Groups. Some others, have had multiple ticket sets and have missed out on Boarding Groups at 7am.
My guess, if you bought your
Disneyland tickets and made the reservations at the same time on the Disneyland website or app, that they would be directly linked. When then wouldn't have an issue with Boarding Groups.
Although if you bought multiple tickets (let's say you got one set of 4 day Park Hoppers and another set of 3 day Park Hoppers both linked in the app) from outside vendors or part of a vacation package (like Costco) and THEN made reservations to the parks.
Maybe with those 2 sets of tickets (3 day and 4 day hoppers from the example above) the Disneyland app can't tell which of your ticket sets are tied to your reservation and doesn't automatically select your party. You would then have to automatically select the names yourself but that delay in selecting the names will cause you that delay in several seconds and miss out on the boarding group at 7am. This isn't as much of an issue for the 12pm boarding groups, as long as you've already entered one of the parks. Which then links one set of your tickets to that reservation.
People who have had this issue have reported that they created a new Disneyland account and have one set of tickets linked on one account and another set of tickets on the secondary account. They said there wasn't any issues with getting BGs after they split them up.