Bookings App automatically updating 'All day' Bookings to span two days

Hi there.  I'm new to this community, so thank you for your help.  I've used the Bookings app for the last four years or so, but recently when I've made an 'All Day' booking as I usually would, I return to it a few minutes later and find that the 'All day' booking has auto-updated to span two days instead of just the one.  This happens when making bookings across my Mac devices (Mac mini & MacBook Air).  I'm the only one who makes bookings, do can't see if it happens to anyone else. Is this a known issue / is there an easy fix?  Thanks for your help!