iPhone calendar events haphazardly working or not iOS 18

After installing iOS 18, calendar events sometime flash up, sometimes not; sometimes with sound & haptics, sometimes not. The same event, with 2 reminders (Default 15 mins ahead, and At Time of Event) might work one day but not the next time. For example, today I added 3 events: the first starting during Do Not Disturb time, the other 2 scheduled almost an hour after Do Not Disturb ends. None of the 3 flashed up on the Lock Screen. I expected the first event would not make a sound (due to Do Not Disturb), but the next 2 should have worked normally. Or whatever is normal for the new Calendar.

Two other events, starting two hours later, both worked.

I cannot explain it. Copying and pasting an event, versus creating from scratch, works haphazardly. Weekly repeating events work sometimes and then other times not. Even if I'm not around to hear the alert, the alert should be persistent when I look at the Lock Screen, until I clear it.

In the past, to make iOS use sounds and haptics, I went into Settings and turned each off/turned each back on; then sounds and haptics worked for a while. This no longer does the trick in iOS 18.

Another idea might be Focus while Driving. For several months I used Driving Focus to silence everything except a select group of contacts, but Driving Focus silenced everything and interfered so much with even hands-free actions in Car Play that I deleted Driving Focus. Unfortunately once having activated Driving Focus, it permanently silences everything once I'm in a moving car, unless I'm connected to Car Play. I don't know whether there is a residual effect of Driving Focus that also switches off certain (not all) sounds/alerts.

Any ideas?