It looks like there is a new "feature" in google that automatically puts google drive forms in "locked" mode so they can't be copied. Since you are an Editor on the form, you will be able to unlock the form so it can be copied. Here are the instructions.
1. Open the document.
2. Click on "Change settings" located near the top of the form.
3. In Change settings, you'll see that Locked Mode is on (red).
4. Toggle locked mode to off (grey), you should then be able to make a copy of the form.
5. If the form you are copying is a quiz for students, once you have copied it, turn locked mode back on, on your copy. This will prevent students from having the ability to open up additional tabs in their browser to look up information while taking the quiz.