Hello Fiona,
This does not appear to be a WordPress issue but the way WordPress CMS functions by default. Each instance in the Hotel Booking plugin is created as a custom post type, therefore, ID’s for them are generated automatically by WordPress. And as you know you can not have two different posts/instances with the same ID in WordPress, each of them has a unique ID generated and assigned to them
There is nothing we can do about it, unfortunately.
Regards,
Andre.