AMB

Please could you tell me why , when I try to group a collection of single plants to create one group, with a single label, all those plants disappear when I click on 'Change Plant Grouping'? It seems to happen after I have been working on a file for sometime. I have tried saving and coming out of it, and then reopening the file, but it still happens. I have also tried going to a previous file, but the same problem re-occurs. Any advice would be very welcome Thank you.