iCloud Calendar one-day events display as two

Using iCloud calendar on my Mac, it displays all one-day events spanning over two days, but it only starts from 1 April 2024, single dates prior to this are all correct. I don't understand why this has happened, especially as my iPhone calendar is correct. I think it started after I upgraded the software to Sonoma 14.2.1?

How can I correct this problem to ensure my iCloud calendar one-day events are displayed over one day, not two? Help! It's driving me nuts.