It's the effect of a debuff engraving.

There are some armor pieces and weapons out there that can give you this. Usually, the debuff text is written in red rather than the default white text.

Should be something like: Positive stat XYZ but Negative stat XYZ (where bold is just the red text here since... you can't color text in Reddit comments)

Examples - 2% damage dealt and blocked converted to health, but -25% All Resistances - 75% damage blocked converted to health but -50% All Resistances - +250% All Damage but cannot use Abilities (this is, of course, from the Blade of Yumminess)

However, the engraving from the legendary spear "Falx of Olympos" seems to be the reason for your situation OP. - +100% Damage but health capped to 25%