Pivot Groups Collapsing in 2016

I am creating groups in a pivot table. The problem arises after I save my data close the program and reopen the document later. After the document is opened the groups are renamed back to Group1 Group2 etc. and collapsed. There is no way to expand the groups (eg. the plus button is missing) and the only way to restore access to the group contents is to create a new group of any data which miraculously causes all the original groups to reappear. Has anyone had a similar situation and if so have you found a solution to the problem?