An earlier process in Pharo which resulted in the appearance of a debugger window seems to be still running in the background and comes up again every time the image is started.

It seems to be have been triggered by an error in a startup process discussed in /a/78722508/172406.

These are the related windows

.

The Process Browser window.

Right clicking the items labelled (40) and (40s) brings up a menu with a Terminate option and I suspect using it will prevent it from happening again.