I personally consider 2% mortality in good conditions to be normal...5% common when water OR air temps are over 75. Some species like crappie, you can lose all of in water or air temps over 60.

Most hatcheries build in the losses with "extras", but since you said the fish swam away and looked lively, I would suspect improper handling and stress during tempering and acclimation was the culprit. 3" RES (or most panfish that size) can be pretty fragile too. 4" and larger are a LOT more forgiving.