Group text uncontrollably changing recipients?

[Android Central Question]

When I switched from a Galaxy S7 Edge to my current S8 Plus, something went wrong with one of my contacts. It seems that two numbers combined (it looks like this: 0001234567,1112233344 instead of a standard eight digit phone number plus area code) when restoring my backed up text messages. I used SMS Backup & Restore to do that job, if that helps. Now whenever I try to text a group including my friend, any response texts to me get sent to a new altered group chat that has switched my friend with the other person (who I would prefer not to contact at all). I have tried everything from deleting and recreating contacts to removing all contacts from my sim card to triple checking for duplicate contacts, all to no avail. In my contacts everything looks normal, and I can make calls without issue. But within all texting apps it shows the long combo-number. Textra somehow allows me to circumvent the issue, but I would like to change to android messages now that they will allow texting from computer. Please help. I am so stumped.