iPhone 16 calendar turns all-day appointments into two-day events

Upgraded recently to iPhone 16. My calendar on iPhone suddenly turned all my ALL DAY appointments into two day appointments. For example April 1 appointment became April 1 & 2. So I was now unsure of which actual date it was on. Discovered if I open the appointment and change something small (for example turn off an alarm or put one on) and then exit… it resets to the original date. Hope this is helpful until the problem is fixed.

[Re-Titled by Moderator]

Original Title: Calendar issue