+1 all maximum resistances Armour Mastery.

Armour Mastery that gives "+1% all maximum resistances if all equipment is armour" doesn't give +1% to maximum chaos resistance.

I would suppose it's bcs of your shield?

But it gives me +1% max ele resistances, just +1% max chaos res part doesn't work.

But it gives me +1% max ele resistances, just +1% max chaos res part doesn't work. It says "+1% maximum resistances", not "+1% maximum elemental resistances", so I think it should give +1% chaos res too.
In path of building it gives me +1 max chaos res, but in-game it doesn't work.

If I were to guess its a wording issue that ggg screwed up. I think I can count on my fingers how many things are "all resistances" vs "all elemental resistancs" so its not something they do often.

Could be bugged but I would wager they screwed up the text.