Did you ever get this fixed?
I did not see your question and went way overboard describing the exact same problem
https://community.plotly.com/t/dash-loading-failure-in-apache-cgi/37013. No one has offered an answer yet.
Setting url_base_pathname should fix it, but does not help me.
It seems that dash engineers and users are all using WSGI, but I’m stuck with Apache CGI and I presume you are also.