@Ahecht wrote:

• Enter wikitext into the text box

Could you provide an example of the wikitext you're trying? Can you retry and see if you get a 502 again, or if you get the error as I describe below?

Above clarification notwithstanding, I can replicate a similar bug by:

• Going to https://refill.toolforge.org
• Clicking Toggle advanced input
• Entering the wikitext This reference can be expanded<ref>https://refill.toolforge.org/</ref>
• Ensuring the Pretend it's from: option is set to en and clicking Fix wikitext

I am taken to this page, where the following error is given:

Submitting your task... The browser (or proxy) sent a request that this server could not understand.

The underlying API request returns:

{
  "message": "The browser (or proxy) sent a request that this server could not understand."
}

Of note, if I go to https://refill.toolforge.org/ng and do the above (this time expanding the USE CUSTOM WIKICODE option) it works as expected — @Ahecht, could you also try doing this?

I am also seeing it only on https://refill.toolforge.org, not the ng site. Whether I get the "request this server could not understand" message or the 502 error seems to be based on the length of the input. If I paste in your example 42 times I get a 502 error, but if I only paste it in 41 times I get the other error page.