are you using a round or square brush?
( no **** got asked this once by rep after contacting their expert when I had similar issues!)
Allot of what your trying is Voodoo I think (we all been there). 2 stage firings, different liquids all that stuff.You didn't say whats going on with your vacuume? your getting proper vacuume? and how much? the whipmix has a way of checking this??
almost certainly not related to yours but I spent years fighting similar surface pitting. In the end it turned out it was contamination from using blue rubber wheels for smoothing surface before final glaze fire. Didn't matter how well was cleaned. Stopped doing this (went to using sand paper cones) and all my problems went away.
using distilled water/build liquid/glaze liquid in ceramic depending what I'm doing.
770. (even higher if your firing on trays and not on pegs)
vacuume- start 650c, through rest of cycle.
about 4-6minute dry,
lisi or emax ceram no different (I use both on the same crowns)
Do that, if you still having issues its the furnace. temps off, vacuume not working properly, needs dehymidifying or a clean cycle to burn all the crap out.