Searching around more, I found that USG's site says Silver Set is available only in the Western US, so I suppose many here won't be familiar with it.

This ^.:thumbsup:but I may quit making this more complicated than it needs to be and pick up a bucket of green lid premix!
The problem is a thin layer over something that sucks the moisture out of the compound before it can dry. Put on a very thin coat of mud, put on saturated tape and trowel it out. Let it dry and continue additional coats.