I recently updated my Mac to macOS Mojave (10.14.1).
I was upgrading my MacPorts stuff, and found that wxMaxima was behaving weirdly – some smallish rectangular scroll frame is overlapping the main window and wxMaxima does not work right.
The display looks garbled and corrupted.
I found a way to make it behave better: show, then hide the History (menu item View – History).
The scrolly thing seems to be a garbled history frame, and show/hiding cleans it up.
Hope that helps someone!