I'm running with icloud messages OFF and Filter Unknown Senders OFF and no joy yet again. Text bug remains. The only thing I've found that remotely works is killing the messaging window after EVERY text which is not feasible even as a short-term work-around.
Also, found yesterday that a known contact that is NOT pinned sent me a text and the alert bug reared it's ugly face.
My text alerts will sometimes work and randomly not work. I'll have unread texts out of nowhere in text windows that my phone thinks they've been "read" even though I didn't know they had arrived as I never got any type of alert. The only way I knew they were missed was because I went to each text window. 🤦🏻♂️