Some mirrors are broken (values missing)

I’m mirroring information from a Contacts board to an Events board. Most of the mirror values show up, but on some rows, the info just doesn’t show up. Even though when I click into the contact, that information is there.
Also, normally I can add the information for Contact through the Event item (& updated via mirror link – super great!), but with these “blank” spots, it doesn’t let me. Which confirms to me that something is going wrong.

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