Extension developers could be the culprit for this toolbar visibility issue.
Many developers still use toolbar.show instead of toolbar.restore, and that’s what causes toolbars to pop up every time SketchUp starts, even if you’ve closed them before.
# Incorrect
toolbar.show # Forces toolbar to appear every time
This is how developers should deal with toolbar visibility…
toolbar.get_last_state == TB_NEVER_SHOWN ? toolbar.show : toolbar.restore
I suspect SketchUp might not be responsible for this issue to happen, but maybe they can enforce developers to adopt the code above and if not then the extensibility team should not approve the extension.