Did they fix the +1 AC bonus for Duel Wielding? Did they fix Two Weapon Fighting (Does the bonus on the offhand work as expected now?)
*You can now apply multiple Hunter’s Marks to targets.* What does this mean? Can you put two or more Hunter's Marks on the SAME target? Meaning 2d6 bonus damage? Or does it just mean you can put Hunter's Mark on multiple targets , what good does this do?

The applying multiple hunter's marks refers to having 2 or more rangers in the party with the spell allowing them to both mark the same target. Before only one ranger could mark one target at a time if a different ranger attempted to mark it would remove the first ranger's mark.

From my testing they fixed the OP Colossus Slayer, before it would deal additional damage based on whatever the bonuses the player had, such as great weapon master giving +10 damage with heavy weapons also applying to the colossus slayer damage. I learned this cause I like playing strength-based rangers.

As far as duel wielding I can't answer any questions with that cause I never tried it.

Thank you very much that makes sense now.