The following commit, currently on master and not released yet, breaks some urls:

Commit: 3b85073
log.Fatal(server.ListenAndServe()) -> log.Fatal(http.ListenAndServe(*addr, nil))

An example url that breaks:
https://imageproxy/signature=/https://domain//proxied.png

It breaks, because the DefaultServeMux, performs url sanitization, which redirects the url to:
https://imageproxy/signature=/https:/domain/proxied.png

A possible solution for those that want to run the profiler would be to run the profiler on a different port number, or opt-in into this behavior. Or a change to how the signing is performed. Alternative would be just undo that commit. I'm happy to help out with a PR.