If you find that multiple bookings have been assigned to the same area in Access Collins and you are not able to tell how this has happened, first check the following.
Check the booking history
Before raising the case, you could check the history for both bookings:
In the Diary, click on the booking.
Click View booking.
Click on History.
In history, you will be able to see if the booking has been manually assigned to the table by a user.
Verify your Tables/Areas
Also check if the table is able to take multiple groups:
Click Settings, then Sites and choose the site.
Click Tables/Areas.
Scroll to the table where the bookings have been placed.
Check if multiple groups is ticked for the table.
If the booking was not added by a user and the table is not able to take multiple groups, please raise this issue with the support team to investigate further and provide the booking details.