I'm getting an error from Portfolio that I have multiple overlapping sprints, but when I look at the sprints, they are not actually overlapping. Is this a new bug or something I'm missing?
The most likely issue is that your sprint DEMETER-RS-26 is in the past but is still active (not closed) saying that it is still running. As a result it is in fact overlapping EOS-RS-1.
If that makes sense, I'd advise to complete the DEMETER-RS-26 sprint and then reload / recalculate the plan to see if the error persists.