Witch 4.5.3 is out, with improvements in Spaces support and smarter logic when switching after you’ve used a combination of Witch and non-Witch actions to switch windows and/or tabs. We also worked around an issue where an app that provides nonsensical information about its tabs could crash Witch. You can read the release notes, but the above is all they say, though in an easier-to-read format.
If you have Witch set to automatically update, you should see the update now. If you don’t have automatic updates enabled, open Witch’s System Settings panel, click on the About tab, and click Check Now.