I currently have three conversation that won't let me reply. Each one only has 2-3 people on it. Looking at all my texts and conversations I can't see any consistency regarding the carrier or phones they are using (Android, iPhone) so I don't think that is it.
Also, I noticed that for Most of my messages and group conversations, each message in it says MMS next to it. When I open the a text or group conversation a very annoying message almost always pops-up at the bottom for a moment that says "converting to multimedia message...". For some reason, this doesn't happen on a few text messages, however. When I open one of the conversation that don't work, I don't get that pop-up.
I wonder if for these conversations aren't working because the app is not converting it to an MMS? Is there a way to force the conversation to convert it to MMS?
I don't think there is any difference with the carrier. It was still an issue when I was in safe mode. There's nothing that I can see that is unique about the afflicted conversations.
I just switched to Google Messages for my texting app. So far, it does not have this problem. I am able to use it to reply to the group texts that Samsung Messages can't. I would suggest that anyone with this problem give another texting app a try until Samsung gets this fixed.
I had one previous group text that came over from my Note 5 that no longer allowed me to send messages...all the other group texts that transferred are fine. Weird. I checked every setring I could think of. The one that wasnt working anymore was one with my parents, so I never tried deleting the chain and restarting because I didn't want to lose our old conversations. Anyway, thanks for the google messanger tip. I switched to that and can now text them again!