I’m experiencing something odd with the Message app. I send a single person a message and that works fine. When they reply, I get their reply in a new/separate chat. Future messages from me and the other person then all appear together in the new chat. Anyone know why this happens? Viewing “Details” for the original message and first reply show they are both SMS messages.
I had a couple of odd issues in the past similar to what you described. While I never really found the direct cause, I did resolve it as follows:
I installed Fossify Message. When I launched it I slected it to be my new default message app. I used it to import my existing messages. I then went into the setting for the old app (e/os default) and cleared the cache, and reset the app settings. I used the Fossify for a couple of days just to make sure things worked correctly, then relaunched the default app, made it the default, and it pulled in all my old messages and that is what I’m using now.