iOS Auto Proxy Protocol Change?

As recently as February, I've used a version of proxyMyPhone, a simple Python server that spits back a PAC file pointing to a SOCKS proxy on my local network. Then, I can go into my iPhone's settings and choose the automatic HTTP proxy option, with `http://<computer-ip>:<port>` as the URL, and browse my phone via the SOCKS proxy.

I've come back to this three months later, and it no longer works. It appears that the iPhone is forcing HTTPS protocol, even if I explicitly prefix my URL with http. Was there a software update that did this? I'm not sure where to look for release notes that might confirm this suspicion. The upshot is my self-signed certificate won't be respected and now I can't use a device on my local network to provide the PAC file. Is this really necessary? Forcing TLS just to exchange a PAC file seems heavy handed to me, but I'll plead ignorance if I'm wrong here.