When the index has decided to replace one counter with another, does the ETF suffer losses? Since most of the time, the counter going to be drop out is likely to be underperform?

As far as I know they do it after market close

with the nominal sell sum minus transaction fees

There is no material difference because any loss is already factored into the price. Unless you're saying that the ETF did not change it components even though the index did, which is unlikely too.