create issue API fails by dropping connection for **some** payloads

[sebastian_popa]

To keep it short, have an automation in place which "dispatches" JIRAs, from some "intermediary" project to "final" projects, where developers are supposed to work on them. The workflow is "find untouched JIRAs in interim project, for each one create a payload for API creation keeping description and so on the same, call issue creation API with the payload, mark initial issue as touched". 

The JIRAs pertain to websites vulnerabilities (XSS and so on), and do contain URLs with scary looking strings (js code, "alert()", unicode chars and so on). Some issues are being created correctly, some fail, hard to pinpoint the exact issue. 

A list of odd and confounding behaviors:

• dug into one of the failing issues, found out that if a URL inside the description ends with a parenthesis (truncate URL after parenthesis) it fails (consistently), if I take that parenthesis out (truncate URL before it), works (consistently)
  • FAILS - 
    ...long URL...%3C%2Fscript%3E%3Cscript%3Ealert(
  • SUCCEEDS - 
    ...long URL...%3C%2Fscript%3E%3Cscript%3Ealert
• when JIRA creation fails, doesn't fail with 400, but get a "The response ended prematurely" in HTTP client call. This kind of suggests that there's another system before hitting the actual API, and this one inspects traffic, if traffic doesn't look good, drops the connection. Worse, if there's some API gateway with WAF protection (with AI?), it might mean that some content cannot make it through
• related, not sure how the initial JIRA in the "intermediary" project gets successfully created, there's some integration from some third-party product I can't look into
• tried both v2 and v3 "create issue" API (/rest/api/3/issue and /rest/api/2/issue), both fail the same way

Any idea what might happen and how I can successfully create JIRAs which contain URLs with "questionable" content? 

Thanks!