A common problem for players who smash a lot is to have trouble lifting the ball against heavy backspin when looping. A common problem for players who loop a lot is to follow their opening loop against backspin by loop-killing or smashing a blocked return off the end. The two problems are related, and have to do with the back shoulder – the right shoulder for a right-hander.
Players who smash a lot often do not drop their back shoulder when looping against backspin (or don't drop it enough). This costs them lifting power when looping, and leads to an erratic loop against heavy backspin. (Often they over-compensate, dropping their arm too much, and so loop too softly or off the end.) Players who loop a lot, after looping against backspin, will often automatically drop their back shoulder for the next shot as well. This causes them to lift slightly when loop-killing or smashing against a blocked return, and so the put-away goes off the end.
So remember this rule: when looping against backspin, drop that shoulder; when loop-killing or smashing the blocked return, keep that shoulder up!