InfoPath Dev

We have a form with VSTA code. The form is full-trust and signed with a code signing cert from GODADDY. The cert has been deployed to 3000+ users with GPO. For "most" users the form works as expected. For a few users, however, the form is "not from a trusted source" and prompts for a smart card and then prompts for trust approval.
Troubleshooting so far...
Verified the cert path is installed
Manually removed cert and ran gpupdate /force
Manually removed cert and manually installed
Installed cert in ALL the stores
Reset IE SSL cache
Completely reset IE
Cleared appdata cache
Republished form
Resigned and republished form
Re-exported .cer and installed again
Reboot
Logged-in as a different users with same results

We're all out of ideas.

So - the last item - logged in as different user w/ same results probably negates this idea, but perhaps clear the form from the InfoPath cache? Open InfoPath Filler, go to the File > New, find the form, right click and Remove (or Get Update) and try again?

>Cleared appdata cache