I wasn’t able to reproduce. The error pages do return the code, though, but I was expecting that. I’m hoping that OP can provide a request that does reproduce it.

Sure thing - there's a link at the top of the post with an example of code. HTML is about 200 lines, each one slightly different, did a 3 second wait before each post request (25 posts, 5 with the offending tracking code), used their python API

Tried with all my might and no dice: https://gist.github.com/joshmn/c87a52b5328aa4f452be7970af4ba...

Now, are _you_ serving from Cloudflare and you're seeing this in production? Or is this coming from the output?

Ah - guess I can reply now here, but HN seems to be rate limiting me - lets perhaps DM on twitter to find repro steps?

But to your main question - the resultant HTML is occurring after running a python script fully locally, no hosting, prod, dev server, or anything related to Cloudflare coming into play.

My email's in my profile :)

That's sampling. Don't inject everytime, just inject 20% of the time.

Cloudflare doesn't have any sampling setting anywhere close to 20%.