On a few user's workstations, I'm seeing an issue.
Though this "Root CA" is in the Trusted Root Certification Authorities Store, for both their machine and their user, IE11 will not trust this certificate.
I can browse to the same site in Edge with no trust issue. Same for Firefox with
security.enterprise_roots.enabled = true
95% of other devices with the same certificate store settings are NOT having this issue.
The only other thing that might be important - my sample testing machine where this is NOT an issue is running IE 11.1006.17134.0 - a machine WITH the issue is running IE 11.1.18362.0. Can't seem to find any helpful information on changes between these versions.
TL;DR: why is my root CA not working in IE but works in other browsers?