Check if you or anyone with webreport access created/scheduled any custom report recently, which is huge in size, such reports can block the functionality of webreport.
I encountered with the similar issue, whenever I was trying to schedule or change any report, but were not receiving any email, later looking into debug logs was able to see newly created report was enabled with such properties which was taking 2hr+ to fetch the content.
Apart from it you can validate your SMTP configuration or clear webreport cache or check any error in webrport.
