Default tooltips blank only on service

I have the exact same issue, all previous reports (prior to 1-2 weeks ago) have all published fine, showing the same dark grey/near black background, white text, tooltip as displayed in the desktop editor. As soon as I then publish a report it's changing the tooltip to a white background, black text. It's also enabling 'Drill up' despite having disabled drill through, header icons and everything else (but only in the white tooltips ?!).

EDIT: It seems that not all visuals are affected, as doughnut visual tooltips appear unaffected (?!) so it's something they've messed around with that isn't related to them.

This has retrospectively effected all reports that have not been published in months and it is NOT desired or acceptable, nor is it practical to go back through the multiple apps, workspaces and countless reports to change every toolip on every report back to what it was and/or should be !

This needs to be raised as a bug and reverted, quickly, otherwise I, and I wager everyone using published reports will have an entire reporting suites/apps looking like they're populated by developers that simply don't care about the overall outcome, hardly very professional...