>>>>Use the developer tools in the browser to see what is actually getting sent.
>>>>
>>>It actually helped to figure out the problem eventually. The http call was wrong from that page
>>
>>Getting a 400 from the WebAPI controller was a good indication of that :-}
>>
>> - not sure how it worked before. I made a fix and it's now working.
>
>I compared the APIController's code versions from TFS Source Control. I found that there was an extra route and method called GetLayouts which was commented out by my colleague and then removed. That's what broke it.

Based on your last post I was going to say that the route MUST have changed.....