Interesting, when I run

curl -i https://proxy.golang.org/github.com/gohugoio/hugo\!test\!modules1_darwin/modh2/@v/v1.4.0.info

I get the following:

HTTP/2 410
content-type: text/plain; charset=UTF-8
date: Fri, 06 Sep 2019 14:42:46 GMT
expires: Fri, 06 Sep 2019 15:12:46 GMT
x-content-type-options: nosniff
x-frame-options: SAMEORIGIN
x-xss-protection: 0
content-length: 61
cache-control: public, max-age=1800
age: 93
alt-svc: quic=":443"; ma=2592000; v="46,43,39"

not found: unknown revision Test/Modules1_darwin/modh2/v1.4.0%

I'm not sure why you are missing the error message when you run the command. Can you confirm that you see the same thing when you navigate to https://proxy.golang.org/github.com/gohugoio/hugo\!test\!modules1_darwin/modh2/@v/v1.4.0.info in the browser?

Alright, I'll use screenshots to make you believe me. 😂

Terminal:

Safari:

And since it's normal on your side, I think this may be a problem with CDN nodes. I don't know, just a guess.

Sorry that was my bad. I needed to remove the backslashes when I put it in the browser :)

Will look into this.

It looks like the mirror had a cached copy of this particular module version which has since been removed from upstream. I can see that sum.golang.org has seen it in the past: https://sum.golang.org/lookup/github.com/gohugoio/hugo!test!modules1_darwin/modh2@v1.4.0

I added a FAQ entry on the https://proxy.golang.org docs to explain this case a little better, and I can look into improving the error message later on.

/cc @hyangah @heschik
(I'll be taking the next 2 weeks as vacation)

Closing this issue because it hasn't been reproduced since the last time.