Thanks for that info and choosing the Apple Support Communities. Based on what you stated, it seems you are having issues with removing a contact from a group message thread on your iPhone. To help with this issue, restart your iPhone and then follow these steps:
Add or remove someone from a group conversation
Anyone in a group iMessage can add or remove someone from the conversation. You can remove a person from a group iMessage that has at least three other people. You can’t add or remove people from group MMS messages or group SMS messages.
Remove a person
Restart your iPhone, iPad, or iPod touch
Send a group message on your iPhone, iPad, or iPod touch - Apple Support
Cheers!
