Receiving random text alerts on my iPhone 16 Pro after iOS 18.6 update

My iPhone 16 Pro, updated to 18.6, only randomly sends alerts that a text has arrived. I checked Hide Alerts on my contacts individually; it is not on. I have reset the iPhone. I have had 6 sessions by phone with Apple Support; not fixed. Alerts ping correctly on my iPad, but only randomly on my iPhone and Apple Watch. Help!

[Re-Titled by Moderator]

Original Title: Text alerts are only random