Revan's leadership reduces the max health of a target with Bonus Protection. There are currently 2 characters in the game that can gain Bonus Protection. They are Enfys Nest and Darth Traya. As @OMEGA_RAZER pointed out, reducing max health should reduce the Bonus Protection, but it is not. This interaction is clearly a bug. Please fix at the earliest available opportunity.
Here is the relevant mechanics on swgoh.gg of Revan's leadership:
You pointed out what the bug was OMEGA_RAZER. Which is that Enfys Nest uses a stat called TARGET_MAX_HP to gain her Bonus Protection instead of Max Health. Looking through swgoh.gg at Traya's Bonus Protection ability it would appear that it correctly references Max Health.
Here is Traya's ability that gives her Bonus Protection:
Enfys Nest on the other hand does not. Here is her ability:
Of the 2 Bonus Protection abilities in the game currently, only 1 is being correctly reduced by Revan's leadership that reduces Max Health.
It's still far from 100% win rate and it's terrible on defense unless you're a really bad pilot of Revan but I digress.
It doesn't need to say initial max health though. Nest's maximum health for a battle and her initial max health are always the same. Her maximum health and her current maximum health are almost never the same in these matches. Her unique is checking her max health and not the current maximum.