I can confirm this. In examining the network activity of the app, I can see that when you tap on the button the join a boarding group from outside the park, the server responds with the list of folks in your party but in that response it states who is in and not in the park.When you continue from the party selection screen, there is no additional network call made, the client just displays the error that people aren’t in the park yet.
Here is the end of the response. I crossed out the 6 guest IDs (my family) because I have no idea how secret those should remain.
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