This bug is specific to a multi-monitor environment where the primary monitor is on the right and you are attempting to place the dialog on a monitor to the left. Closing and re-opening the dialog moves it back to the right (primary) monitor.
Sketchup records the Left: position of the dialog as a negative value (as shown in the PrivatePreferences.json file) when you move the dialog to the left monitor. However, it doesn’t appear to handle a negative position when opening the dialog and moves it back to the primary monitor.
The old WebDialog class handles this situation properly.