We did not have the parallel sprints setting applied, but historically I have always been able to open new sprints from a board with no active sprints, even if there were other active sprints on other boards.
Today, I got an error message that I could not open another sprint because we had other sprints open, even though there were no active sprints on the board I was working from.
I was able to temporarily resolve my issue by applying the parallel sprint setting, but I'm curious if something else changed or is broken in JIRA. I have never had the parallel sprint setting applied, and have always been able to have multiple different sprints open across separate boards.