Group Text Messaging

Suddenly, not all group text messages go through. It is very odd. I can text message anyone privately. Also, some text groups do still work. I have one group with 5 of us on it that does not work, but the same group minus one member, does not work. Suddenly a small text group of 3 of us stopped working. I can receive some messages from a text group of 6 of us - but I can’t reply. Seems to be very random and sudden. Everything worked fine yesterday.

Any ideas?