Why is Hide Alerts not working consistently in group texts on iPhone?

I have Hide Alerts set in a couple of group texts. It has always worked great until the last month or so. Now it works most of the time and then randomly I start getting alerts from a text group I have it set on. When I go to check the setting it is turned on. I have to turn it off and then back on for it to start working again. It does this randomly and usually when I don't want the alerts to come through. Why is it alerting when I have hide alerts on?