Is my form corrupted?

I have a complex form (about 75 questions) which all works fine except for one question which is not behaving properly. Firstly, it does not appear in the form preview. Secondly, it is in the wrong position in the form design but cannot be moved: using the Move question arrows has no effect.

Is the form corrupted and, if so, is there any way to recover it to a working form? Because of its complexity I am reluctant to start again.