I’ve been getting a lot of this lately. It may be related to using multiple tabs. Once it starts I have to restart OmniOutliner to get back to normal where it responds quickly to my key presses.
If there’s anything I can do to debug this, let me know.
My MacBook Pro 2012 seems to be having problems across the board. Rainbow wheels every day in Xcode, Safari, others. So it may be that whatever is happening in OmniOutliner - people with newer machines just don’t notice.