Hello Geoff,
For us, it had something to do with the Nintex update. After the update was completed, I included the .js file link within the settings of the form. You may have to put the entire URL of the Style library location where your .js file is stored. If you actually analyze the .js file, you'll notice there are 6 functions. The bottom 4 functions make up the top 2 functions. You'll only ever need to use the top two functions: EnableConditionControlOnView(parameter) and DisplayControlConditionally(parameter 1, 2, and 3). The EnableConditionControlOnView() function takes a parameter of whatever js variable you want to affiliate to your selection control; radio button 1, 2, or 3 shows panel 1, 2, or 3. The parameter in EnableConditionConrtolOnView(Me) is placed in the second parameter section of DisplayControlConditionally(1, Me, 3). Mainly, you are going to use DisplayControlConditionally() to set up your CSS class, JS variable,and your display condition. You just have to use those functions in the Custom JavaScript section to set them up. Remember, everytime you want to add a new choice control to select a panel or display a panel, you always have to call the function AGAIN, and set up your parameters again for however many panels and choices you have. Don't forget to put those lines 1|, 2|, or 3| after each choice selection. It has something to do with the displayCondition (the third parameter for DisplayControlConditionally().
I hope this helped a little. My biggest suggestion is to look at the .js file, at the 6 functions. The bottom 4 make up the top 2. The top two are called in the Custom Javascript section. Look at the affiliation between the .js file and the downloads.