I think the keyword here might be "between". Are you saying that you position the volume dial between two clicks? If so, then there is no faults as such with the volume control since it is a stepped attenuator and should only work and be used on the clicks, not between them.
^THIS. I was a bit freaked out about this initially and it is indeed the way a stepped attenuator works. And the biggest advantage of this bulky attenuator over a normal POT is that ALL volume ranges are usable - no imbalance at very low volume with is typically the case for POTs.
I'm using the extremely powerful DIY board to drive the TG334 and been using volume 1 or 1.5, and even at 0.5 at quiet places and there is no channel imbalance or any other issue at such low volume settings.