Since two weeks, sandbox 'Refresh' button has disappeared in all the 3 instances we have. Does it have anything to do with the Summer 16 release? I checked with my friends working in different companies and they do not have any such issues. Any one else having this issue?
You may want to raise a case with Salesforce. This usually happens when you run into a Licensing issue or number of sanboxes (specific to full box) available reaches to 0. We had this issue before in one of our client org where it was part of Veeva.
We could get this resolved with a case raised with SFDC.