Found the problem. I think my issue was understanding the top level
config file structure, which consists of:
In the Bitnami distribution, there are actually two of each of these
files. The ones in /opt/bitnami/nginx/conf/bitnami should include the
content from the files in the ~/apps/conf directory. Easy enough.
What's not obvious however is that each installed web app on an instance
must either be setup as a "prefix" or as a "vhost". Mixing the two for
the same app results in very unpredictable behavior.
Feel free to pass this along. A little documentation would have saved me
a bunch of time.