I finally had a chance to follow up on Richard's suggestions for making the AuRacle AGT 2 gold test work more reliably.
I actually did 3 things
Switched to my IPad, was originally using an I Phone. (Don't think this made a difference, just something I did)
Made sure that the microphone jack was set to maximum volume
Made sure that the pen tip was wet by dabbing it on paper towel
Then I calibrated it with the 14k calibration disk
I then began testing on gold samples that I had that were a known karat including 10kt, 14kt, 18kt and 22kt.
I did over 75 tests. I re-calibrated twice when the device told me to.
100% of the tests that I did were accurate / correct.
I think that the other times I used the AGT tester, I may have had the speaker volume full volume rather than the microphone/headphone jack and I may not have paid enough attention to making sure that the pen tip was wet for each test.
So thanks Richard for helping me with this issue.