Group iMessage Conversation Keeps Muting Itself on iPhone

For the last month, one group iMessage conversation on my iPhone repeatedly mutes itself. I'll unmute the conversation and typically receive one new notification before the conversation remutes itself. Sometimes I'll have replied, sometimes not. Sometimes mere seconds will have passed, sometimes a couple days. But the conversation always remutes itself, and I often miss messages.

There are four people in the conversation. I have separate individual exchanges going with all three of the other participants. None of those conversations have ever muted themselves—just the group conversation. No other group conversation has ever muted itself . . . though now I'm afraid to mute another for fear of never being able to unmute it and have it remain so.

I've tried:

1. Unmuting the conversation from my list of conversations (swipe left, tap unmute).
2. Unmuting the conversation from within the conversation (get info, then unmute).
3. Restarting my iPhone.
4. Restarting my iPhone and my Apple Watch after unmuting the conversation on both devices.
5. Unmuting the conversation on every device and restarting them all.
6. Varying the order in which I unmute and restart all my devices.

None of these have worked.

I have not yet tried:

1. Leaving the conversation and asking another participant to re-add me.
2. Resetting my iPhone entirely.

I won't refuse to do these things in the long run—they shouldn't be necessary to unmute a dumb, mostly jokey conversation—but I don't want to lose the conversation history. According to another thread on this topic (inaccurately marked "solved"), people with more important group conversations are resorting to these measures, but they shouldn't have to. The mechanics for muting and unmuting a group conversation are not functioning correctly, and I'm definitely not the only person experiencing this. It's clearly some kind of bug.

Any suggestions? Apple? Anyone?