It appears to me that you
reported the problem to isso developers in September. They recommended you use loopback rather than a Unix socket, since loopback worked.
These examples of OpenBSD's httpd(8) with uWSGI use loopback, rather than Unix sockets.
As I perceive the problem, you have two possible circumventions to your problem.
- Use loopback with httpd(8).
- Use www/nginx as proxy webserver.
I do not understand why neither circumvention is an acceptable solution to the problem you have had for more than 3 months.