Setting a Custom Date Range not working as normal

I usually set the variable date range to cover the length of my process + a couple of days and this is typically 3 to 4 weeks long. I have been doing this for years now and select Custom Range then calendar icon and select start date and then finish date, then Update. This always works but now selecting a 3 week time period of today 00:00 to today+21 days 23:59 and Update it selects only Today 00:00 to today +1 day 23:59.
I Can’t understand why this is now occurring, pleas can you assist?
I have tried Google Chrome and MS Edge browsers and both respond in the same way.