Running Catalina (10.15.6) My SOCKS5 proxy is a
DynamicForwarddeclared port on a ssh session.
My pac file is ultra simple and tested good using online test tools, as well as Chrome which uses the OS's PAC setting.
To eliminate a filesystem sandbox issue, I host the PAC file using a python SimpleHTTPServer. I can see the file being downloaded when I configure it in Network prefs, as well as when I launch chrome and safari.
For some reason, Safari doesn't use my proxy. If I configure the proxy address and port directly under "Proxy" in network prefs, safari uses it fine.
Any clues or troubleshooting suggestion is welcome!