Porosity and really bad casts. Is it investment or something else.

[JeffP]

Hi. Still struggling here.
Attached are photos of my issues


I'll try to be brief. Sterling silver metal. 50% new, 50% used.
3d print of Jamghe castable resin. Also tried Phrozen purple. Cured resin as per recommended. The print is perfect.
Plasticast invest. Following recommended everything. Deionized water. Temp 22-24 C. Followed times and degassing.
Burnout @ 730. Followed Plasticast recommended schedule. Have varied with longer holds and even higher temp.
Kayacast casting machine. Furnace melting. No borax as graphite crucible. Cast as quickly as I can.
But a lot of porosity on some, and less on others.
I'm at 700 M above sea level so suspected the vacuum.
Spoke to Kayacast as the machine doesn't get to 29 but we've eliminated that.
A new suggestion is the investment. I've had it for about 4-5 months. It has always produced light brown staining as shown.
No idea what causes that. It doesn't change, regardless of the burnout schedule.
So I'm at a loss about what to try next.
Any help would be extremely appreciated.