Jira 7.13.1 Server responds to my REST POST with HTTP 500

Is there any reason anyone knows why Jira would 500 on this?

It’s an authenticated POST against /rest/api/2/search.

{
  "fields":["status","assignee"],
  "validateQuery":false,
  "jql":"KEY IN(SPIELSOFTW-2)"
}

I don’t have access to Jira logs. Jira 7.13.1 Server.