I completely wiped away everything and started ground up with Server 2016 and IIS. I installed PHP 7.2, MySQL 5.6, PHPMyAdmin 4.8.3, and WordPress 4.9.8.
I did all the manual configuration required for each. Installed the theme/plugins again. This time buddy press installed correctly with all the directories needed to access messages, etc.
The only thing I did differently was change from MySQL 8.0 to MySQL 5.6 and enable some extensions. I followed this article to the T:
Yeah, Apache seems to be the way to go with WordPress? My boss just likes IIS… I have researched and debugged various things and done fresh installs a few times but I have not tried using buddypress with a different theme and manual user creation. I will try that and report back. Thank you for the tip!