Since you are using Proofgrade, you might want to check a couple of things - the acrylics tend to cut through without some of the issues that you can see with wood.
You might want to try this suggestion from @Rita for your next tests:
https://community.glowforge.com/t/med-pg-acrylic-not-cutting-through/12875/2?u=jules
(Post the results here so they can see them, along with the time again - that was good.)