File association is broken, yes. And it appears to be a general iPadOS problem, not just related to iPadOS 13, because I haven't upgraded to v13 yet. Uninstalling and reinstalling Sketch did nothing for me. Instead it seems, for me at least, to be related to Affinity Designer (or Artstudio Pro), but I am not going to uninstall either to test it. That leaves two common denominators: iOS/iPadOS and Artstudio Pro.