It sounds like you upgraded your operating system to a newer version that isn’t fully compatible with OmniOutliner 4, which originally shipped 12 years ago (in January of 2014) for macOS 10.9 (OS X Mavericks).
First, to clear up a misconception in that final sentence, we never charge full price to customers who have already licensed our apps: we always make the latest versions available at a 50% discount to existing customers (i.e. at half price).
Yes, that’s a bug in the operating system’s compatibility with earlier versions of itself. Apple could fix it, but they’re unlikely to. We do update all of our apps every year to fix compatibility issues with the operating system updates that ship each year. But those fixes are always for the latest version of the app—and OmniOutliner 5 shipped nearly nine years ago, so OmniOutliner 4 is missing a lot of those updates!
(It’s a good day to be upgrading, though, since OmniOutliner 6 just shipped today.)
