Originally Posted by Road Fan

First, I wonder if your high travel stop is too tight. Sounds like you are pressing hard on the paddle to shift the bike and get to that last click.

Then, the cable should never be loose, and the lower travel stop should never let the chain slip off onto the bottom bracket housing.

Within those, if the derailleur is QS and the Ergopower lever is QS, it should be working right barring small tension adjustments.