We have had a number of reports of an unresponsive GUI from macOS users that also have a "window manager" app installed, such as:
- Zoom, and
- Right Zoom.
With Moom, disabling the Move & Zoom when dragging a window to a display edge or corner feature resolved the issue. For Magnet, we have not yet identified which feature is causing this so disabling the app is the only known work-around at this point.
To manage these accessibility apps open System Preferences under Security & Privacy and the Accessibility list.
In general make sure you are using the latest version of any of these apps. Some users have reported the issue and then found out there is a later version that resolves it.
Update: The latest Magnet version fixes the previously broken Ignore DbVisualizer functionality. Ignoring the DbVisualizer app will prevent it from being sluggish while Magnet is active. The side effect is however that Magnet will not work for DbVisualizer.