I've been letting this run for a bit, so I can now let you know that your first suggestion to make changes to /usr/local/nagiosxi/html/includes/components/nagiosbpi/api_tool.php has resolved the problem.
Thanks
BPI Configuration Corrupt and Hostchecks Report Unknown BPI
Re: BPI Configuration Corrupt and Hostchecks Report Unknown
That's great to hear! We'll keep an eye out for your update.