Inconsistent Sound Alerts for Messages

I have an iPhone 15 Plus. Text messages alert me by sound only some of the time from any of my contacts. For example, I'll get a text message from someone without a sound alert...then later I will get a text message alert from that same person with sound. It doesn't matter if the phone is in lock screen or not. It's completely inconsistent and doesn't make sense. I've tried everything, but can't figure it out.