Bing Maps renders all shapes on an HTML 5 canvas which ends up flattening images and disables any animation they might have built in. In this case its likely only rendering the first frame of your animated image which may be the reason why it can't be seen. There is a way to add support for HTML based markers in Bing Maps which would be able to render these images as shown here: https://bingmapsv8samples.azurewebsites.net/#Html%20Pushpin%20Layer but requires a decent amount of external code to be added to your project.
Another option, if you are still early in your development is to consider Azure Maps. Azure Maps supports HTML based markers natively, so using your animated image would be fairly easy. Here are a couple of examples:
https://azuremapscodesamples.azurewebsites.net/?sample=Draggable%20HTML%20Marker
https://azuremapscodesamples.azurewebsites.net/?sample=CSS%20Styled%20HTML%20Marker