MMS Group MMS Corruption: members dropped in replies, Phone numbers changed, New Groups started

Two phones on our TMobile plans experiencing this issue.

Group MMS threads keep getting corrupted. When receiving messages, all group members are present, but replying in that group message, messages is randomly leaving out people, and a NEW message thread is created, with one or more recipients removed. This happens on both the sender's phone and the recipient's phone.

Sometimes replying to the new corrupted thread is not possible, even though messages come in to that corrupted thread. You have to hunt for the right message thread to reply to.

Sometimes Phone numbers are getting corrupted, and digits in the numbers are off. We get a message from a contact, and their number is wrong. We cannot reply to that number, we have to go to the thread with their CORRECT number and reply to that.

This is totally frustrating for everyone, as you can imagine.

Tried uninstalling Messages, deleting most messages, rebooting, reinstalling messages, etc. The problem disappears then comes back.

Samsung phones, with latest updates.