When you try to view a report generated by an old version (such as 2012) of SQL Server Reporting Services instance in a browser other than Internet Explorer or Edge you might notice that it’s displayed as an empty page.
What’s the real solution then?
I personally rely on the small button named Export and looking like a Save as. Which most of us would tend to not even see when the report contents looks “so” empty. But it’s still there in the toolbar. And it can still generate a proper PDF file with the same report contents that is (not) displayed on screen. You’ll just need a PDF reader then to open it.