You over the limit on users in a group and your model listed should show Classic so here are the limits on a blackberry and ATT may have limits on the number a group can send also.
Also no need to double post questions
•On BlackBerry 10 OS: •BBM version 10.2.X or earlier supports 30
•BBM version 10.3.X or above supports 50
•On BlackBerry 7.1 and earlier: •BBM versions 8.1 or earlier supports 30
•BBM version 8.2 or above supports 50
It's most likely that not such a lot of individuals do cluster texting. For me, mix solely sends broadcasted messages, it cannot send a gaggle text even though I reply to a gaggle text. Odd behavior.