i m getting 10 to 45 % invalid share on exp and hasrate is 4x lower than it should be

i have 3 computers with 2 gigas memory , i was checking wish one was making the invalid shares because 2 computer have a not stable gpu,
 but looks like it s all computers, must be something wrong with pool ?

i move 1 than 2 than 3   too musicoins  there hasrate looks normal and leszxs than 2% invalid shares
but when come back to exp it happen again

than i have rx series on multi algo and when they switch to etc   same thing happen low hashrate and invalid up to 30% sometimes, on eth&etc i never see invalid shares