Blizzard have explained that the recent increase to boss health in Fated Raids was actually just a visual bug, related to the spell scaling issues with player and boss health that was fixed earlier today, as noted in the hotfixes.
Fated Raids (Source)
As we’ve examined this and related issues, players noticed our fix seemed to come at the exact time bosses’ health appeared to go up.
We’ve looked into this very thoroughly, and it looks like the issue with spell scaling was also causing enemy health to display incorrectly. The same fix that addressed player abilities like Blade Flurry and boss abilities like Soul Spikes behaving incorrectly, also fixed how enemy health was displayed.
Looking closely at logs of raids before and after the fix, we believe that the effective combat time and difficulty of the raid has remained unchanged.