I've got a Kolpak walk in freezer that has a few, 5 to 10, icicles forming at the inlet air intake starting about 4 to 6 inches up from the wire grill on the condensing unit side of the housing and forming down a few inches below the grill.. I have sealed every opening, electrical, evap. housing cover, etc. The only area not air sealed is the drain line from the pan out to the condensate pan.
The unit has VERY LITTLE coil frost build up and the entrance into this box is through another walk in cooler.
We were getting build up around the evap fan shroud, but the additional sealing has appeared to take care of that.
The entire "unit" gasket looks like its okay. That's the only other guess I have where air is coming in at.