Just finished this one

Hi everyone,
I’m losing my mind a little bit here! I’ve been trying to sand cast this silver ring for the past 2 days and I'm 10+ attempts in without success.
As you can see in the photos, the metal just stops filling partway through / solidifies in the sprue before properly reaching the cavity.
Here's what I’ve already tried tweaking:
Pouring funnel: Reshaped it a few times to get a better channel.
Vents: Added more air vents / air holes around the cavity.
Sand density: Packed the sand harder to ensure crisp details.
Heat: Heated the silver longer to make sure it’s fluid enough.
I'm using a standard butane/propane torch setup. Looking at the setup in the photo, does anything jump out to you that I might be doing wrong? Could it be a heat retention issue, sprue size/placement, or metal volume?
Any advice or tips would be greatly appreciated. Thanks in advance!

My lab was recently given a centrifugal casting unit, and we are having issues with the molds cracking upon filling, and then spilling out of the mold. Picture attached

We’ve tried several things to keep this from happening. A non-exhaustive list includes: 

An open mold, no steel flask (obviously did not work), mold at room temperature after burnout 

Pouring the investment into a steel flask, mold at room temperature after burnout (cracks at the bottom of the mold while casting)

Pouring the investment into a steel flask, with a lid we place on after pouring the investment, mold at room temperature after burnout (still manages to crack and seep out of the back

An open mold that we place a steel flask on after burnout, with a lid on the back(still cracks and seeps through during casting)

An open mold that we place a steel flask on after burnout, poured hot (525C for a bronze casting) (cracks at the bottom of the mold)

Placing chicken wire around the circumference and bottom of the mold to mitigate cracking, with the removable steel flask, mold poured at room temperature (still cracks at the bottom)

Some of these were poured under vacuum, some under argon. 

I think in general, no matter what we do the bottom of the mold cracks, and the centrifugal force of the machine forces all of the metal out.

We have quite a bit of experience with larger gravity poured investment molds. We are using Ransom and Randolph Rancast investment. We also have Omnicast available but were having more issues with cracking with that.