Gap in headset dust cover--what am I missing?
I think the answer is that the Range stem needs spacers with an outside diameter small enough to fit inside the &quot;shelf&quot; ridge inset into the top and bottom of the stem (the depression that Andrew noted in his comment). This shelf is perpendicular to the steerer axis, not sloped, so any spacers properly seated on it will be flat and flush. This also means that at least one spacer is required beneath the stem, as it looks like the headset top on the Rockhopper will not seat properly in that shelf.
Here's a view of the PNW Range stem I found online that clearly shows the shelf:

Just for reference, here's a promo photo of the stock Rockhopper 2020 from Specialized:

If you click to open the image and zoom in, you can see that the headset top is flush with the headtube top, and the spacers above that along with the stem all seem to be flat and flush.
This is consistent with Criggie's observation that the OP's bike photos show a stem with curved bottom and top surfaces, which suggests the root of the problem.