In The Force Awakens, there is a scene in which the main characters are planning on poisoning a group of stormtroopers because Finn states that the armor does not filter out poisonous gas.
However, according to this answerthis answer stormtrooper armor contains:
A vacuum suit with a 20 minute air reserve, as well as possessing air filters for providing protection against airborne pathogens or gas attacks when air was available.
So what happened to the armor in the last 20-30 years between Galactic Empire and First Order to lose the filtration?