I put a double tape between my SIM and the StealthSIM, and it prevented the two from making proper contact. The 0.02mm or so of the tape's thickness was making the connection flaky, so i removed it. Now The two pieces are sitting in my iPhone without help, and my phone's been working fine, so far.
The only one problem I have seems to be that every once in a while, the connection would cut out and my phone thinks there's no SIM, but promptly gain it back. This is shown by the StealthSIM request to display notification and (the screen that displays serial number) being shown. Anybody else get this? In 4 days, I've gotten this maybe twice.