S8 won't send group messages to iPhones

[Bowhunt24]

So this seems to be the opposite of a more common issue. On my mom's S8 (on AT&T), when sending group messages that include an iPhone, the iPhone never receives the message. We've played with all different combos. 1:1 messages work fine to iPhones, group messages on all androids work fine. But whenever it's a group message, any iPhones on that thread don't see her messages. BUT they see the other replies. Any ideas?

Thanks,
Evan