Case Count blank in reports after migration to 8.4

As above, we have a suite of reports, recently migrated from 8.2 to 8.4, and in some of the reports, Case Count has randomly dropped out ie not displaying anymore. We have checked it out and everything appears as it should be - the logic is identical to other reports in which case Count is still working/appearing.

I was told this could be due to the migration to 8.4, specifically ‘SQL optimization’…?

It is really frustrating and even in some reports where we have deleted the original Case Count, and re-entered it, it still is blank in the output. In other reports with multiple tabs, one of Case Counts appears blank yet the others still display (and with the correct value).

Anyone have any suggestions?