I've come across JQL error that has me stumped. I created some simple JQL for a scrum master to find stories in the current sprint for a given project. This made use of this syntax: "sprint in openSprints()". This works fine for me but returns the error above for other users trying the same syntax. I am a Jira system admin and the other user has a standard user role. BTW, there is no sprint with id 8. That does not auto-populate the way sprint with id 1 does. Sprint id = 1 has issues in it as well so the error message might be a red herring.
