Bing Maps truck route API not returning waypointsOrder node when called with OptimizeWaypoints=true

Hello,
we are having this issue since today October 10:

even if we call Bing Maps Truck Route API specifying the OptimizeWaypoints option, the response JSON won't contain waypointsOrder node. This happens randomly (sometimes the node is present, sometimes not).

Here is my test call (I removed the key value):

http://dev.virtualearth.net/REST/v1/Routes/Truck?&wayPoint.1=54.172417,%20-1.360044&wayPoint.2=53.53167725,-1.15774095&wayPoint.3=52.78152084,-1.19816697&wayPoint.4=53.53035355,-1.40961695&wayPoint.5=54.60403061,-1.57016206&wayPoint.6=52.4922142,-2.12309909&wayPoint.7=52.21483612,-2.73221207&wayPoint.8=53.3309151,-1.3369674&wayPoint.9=53.81967545,-2.41687393&wayPoint.10=53.47360611,-2.11940289&wayPoint.11=55.08987808,-1.61527503&wayPoint.12=53.74648285,-0.230272&wayPoint.13=53.52891541,-2.17321491&wayPoint.14=53.52891541,-2.17321491&wayPoint.15=53.4449234,-1.33681703&wayPoint.16=53.88576126,-0.83744103&wayPoint.17=52.65775299,-2.02423191&wayPoint.18=52.14622116,-0.194015&wayPoint.19=53.68714905,-2.46062493&wayPoint.20=53.68714905,-2.46062493&wayPoint.21=54.172417,%20-1.360044&OptimizeWaypoints=true&optimize=time&distanceUnit=km&dimensionUnit=m&vehicleHeight=4.2&vehicleWidth=3&vehicleLength=16&key=[key]

Can you please help?
Thank you
Emanuele