There are many reasons why you might have unallocated booking:

1) Changes to Diary

ResDiary has a built in fail safe for your bookings - so if you make a large change (i.e. disable a service/area/table) and there are bookings that belong to that area it will pop them into the Sidebar.

This is to alert you that this booking has nowhere to go and they need to be re-seated.

2) Un-allocation Tool Used

You can un-allocate your bookings and re-allocate them in order for the diary to shuffle your bookings and replace them in a better order by the rules in your settings. 

See this article on using the Shuffle tool

How to Re-allocate These Bookings

1) Make sure you have the sidebar expanded by pressing this button   at the edge of the screen

2) Then press the  button that then pings the bookings back in by your setting preferences

Unable to Reseat?

Some bookings will get 'Stuck' because they cannot find anywhere to go.

 Click the booking on the sidebar - this then opens the booking screen

Pay attention to:

- Any error messages as this will indicate why it's not going in:

- Check the areas and try again changing the area to 'All Areas' and search again:

- Check the table - is the table still enabled in the diary? Is there no join to support it?

- Time - has this time been removed from the diary?

-  Is there a rule in place for this specific time preventing the booking from being made?

- Service - has the service been removed from the diary?

Those are some of the reasons a booking cannot be re-placed, it is important to look through your settings to check everything is in place to accommodate the booking.