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I am not able to see the screenshot that you attached but since you refer to this form of yours I can see what the issue is. On your matrix fields you opted to use radio buttons and when an option is selected it can no longer be deselected.
It is actually the way that radio button field works. It allows at least one selected option at a time and once it is selected it can not be deselected unless you refresh the page or put a "Reset Form" button on your form.
However, I suggest you to use check boxes instead of radio buttons. They are able to be deselected. Please see how you can change the input type to check boxes:
Select the matrix field on your form builder and click input type above:
Select "Check Box" and you are done. I hope this helps.
Please contact us again if you need any further assistance.