Hi Daniel
How bizarre! I thought this was interesting as I use forms a lot - but never noticed. And upon checking you are absolutely correct.
I sent out a form the other day, amended a question - look at what has been created.

So how I solved this was to go back to the form and select responses > ellipses (...) and then Sync All Responses to a New Workbook. This creates a new excel in the Files Tab

Open that new workbook - walla, no old questions. You can now go delete the old workbook.

Hope this helps.
Best, Chris