What powder? What weight? If it's a flake powder below about 4.0 - 4.4 gr. you will have variation, but always on the low side.
Unless you weigh every charge under those circumstances you will have an occasional light charge get by. Visual inspection is the only practical way to do it for volume handgun loading.
And it's not just Lee equipment--why do you think so many Dillon 550/650 owners put a powder check die in the tool head? I had the problem in spades with a Dillon powder measure trying to load light .38 Spec. ammo. Finally switched to ball powder and it ceased. Same with any cavity/volume dependent charging device at lower weights--beware of flake powders!
Lee even warns about this in their instructions for the Auto Disk measure.