If the landing isn't stable you can always climb a few feet, let the aircraft stabilize, and then attempt the landing again. If the aircraft won't stabilize the conditions are horrible or there is a problem with the stabilization/control of the aircraft.
Humidity shouldn't be a factor unless you're flying inside a cloud or rain. Wind can be an issue but it takes a LOT of wind to be an issue.
Humid air is less dense than dry air, so maybe the props were having to work harder to get a good bite to keep it stable? Naaaahhh.... jk... when mine sways close to the ground it's usually because I'm too heavy-handed on the sticks, trying to counteract the wind