If you're using macOS Catalina and Witch isn't launching on login or reboot, here's the most likely cause: When you installed Witch, you installed it for all users. This is done via a macOS-provided sheet that appears when you double-click Witch on the downloaded disk image, and it looks like this:

When Witch is installed for all users—using the bottom radio button in the above image—then it will not load on login or after a reboot. Instead, you'll have to manually enable it each time.

We've investigated, and unfortunately, this appears to be a macOS issue, not a Witch issue, so we can't change our code to make it work. In the short term, the solution is simple: Uninstall Witch (right-click on its System Preferences panel and select the only option that appear in the contextual menu), then reinstall it for the current user only. If you need Witch for more than one user on your Mac, install it separately for each user.

Due to this and other issues with third-party System Preferences panels in macOS Catalina, we are in the process of converting Witch to a standalone application. When that conversion is completed, there won't be any issues installing Witch for all users (because applications are generally available to all users by default). Until we get the app released, however, please install Witch only for the current user.