Yes, I am using the HKLM registry settings to lock down these settings -- using the most restrictive ones documented in Enhanced Security — Acrobat Application Security Guide.
I worked methodically through different options like eliminating the Customization Wizard, rolling back to the Adobe download and installed with defaults and then updating the settings minimally, using different patches, etc. Looks like the issue is due to our using IE's Enhanced Protected Mode. If this is disabled then Acrobat's Protected View works properly. Obviously, turning EPM off is not an option and frankly I cannot believe in 2018 Acrobat still does not support security controls provided by IE that were created YEARS ago. Reader's Protected View works perfectly so the only solution I see is to deploy Reader to the Acrobat systems and then tweak the file settings to use Acrobat outside of the web browser.
EPM in registry:
HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Internet Explorer\Main"Isolation"="PMEM"