I modified my c2runtime.js
and overrode the default onErrorOccurred for the MicrosoftNSJS.Advertising.InterstitialAd.
Open c2runtime.js press Ctrl K+D it will format the code for you.
search for MicrosoftNSJS.Advertising.InterstitialAd
Replace the function with the below code.  Put a breakpoint in errorOccurredHandler compile for debug.  I was able to see the error message that at no Ads were available.
When I replaced my AdUnitID and ApplictionID in index.html and data.json with the test ids.  I was able to see test ads.  I don't think they showed up without the code change.  But I didn't run it enough to be sure  
https://msdn.microsoft.com/windows/uwp/ ... ode-values
    u.prototype.aT = function (f) {
        if ("undefined" !== typeof MicrosoftNSJS) {
            this.we = new MicrosoftNSJS.Advertising.InterstitialAd;
            var q = this;
            this.we.onAdReady = function () { q.j.trigger(hh.prototype.q.ur, q) };
            this.we.onErrorOccurred = errorOccurredHandler;
            //function () { q.j.trigger(hh.prototype.q.tr, q) };
            this.we.onCompleted = function () { q.j.trigger(hh.prototype.q.sr, q) };
            this.we.onCancelled = function () { q.j.trigger(hh.prototype.q.rr, q) };
            this.we.requestAd(MicrosoftNSJS.Advertising.InterstitialAdType.video, this.EU, f || this.uU)
        }
    };
    function errorOccurredHandler(sender, args) {
        console.log(args.errorMessage);
    };