Are you playing the 1st Divinity Original Sin? The "Enhanced" Edition is for the 1st game. For the 2nd game it will be the Definitive Edition.
Both Blitz Bolt and Treat Poisoning are from the 1st game, but I didn't notice in your other post.
First Aid and Treat Poisoning are combined into one First Aid in the 2nd game that cures all effects the other two spells did in 1st game.
Having 100% poison resistance doesn't prevent poison from being applied. The character just doesn't take damage from it. Pretty sure if it goes over 100% they would heal from being poisoned instead.
