It appears that ever since the X/Cornerstone update that included the new access control permissions assignment functionality, non admins cannot save header options/updates. I see there was a fix for a header saving issue for Pro 2.3, but no such fix for for X. They may be totally separate issues.
All I am sure of is prior to the new built in permissions settings, all I needed to do was assign the edit_theme_options permission and a non admin could save the changes. Now, even with all permissions assigned to a role in the X access control settings, the header cannot be saved.
So far, the only issue has been with saving changes to the header. Everything else seems to function correctly/ Hopefully the developers didn’t use the the native manage options capability in WordPress to validate against. That capability really isn’t appropriate.
Thanks.