my base and i had the exact same problem!
everytime we just popped of we would heard a loud thud and think 'was that us?'
and i talked it over with him and he decided to change his grip.
when we popped off he usually followed my hips down to the ground and that was when it was a hard landing. so he changed his grip so when he popped me off he pushed a little higher and catching with higher arms he catched and followed my bum to the ground while i held onto his hands for a bit of stability to ease the landing. This helped so much! also have you talked to your flyer about it? because sometimes if she is land heels and toes at the same time instead of toes than heels or heels then toes it can give the impression that she is hitting the floor much harder because she cant absorb the landing.