After creating a custom element in Generator, saving it and trying to edit you do not see the edit controls. Instead, the element is displaying as in View Mode (rendered), and there is no possibility to edit it.
Issue with ShortPoint Generator which is currently being fixed. We will send you a hotfix package after the issue is solved.
Build custom elements inside an empty test page on your environment. Then, copy them into the Generator after everything is ready. You will be able to edit the element normally, and then paste it into the Generator after you are fully happy with the result.