got passed the issue by setting the custom asset manager to the spineCanvas instance, but let me know if there is a better practice!
const appInstance = new App();
const spineCanvas = new spine.SpineCanvas(canvas, {
pathPrefix: '/',
app: appInstance,
});
spineCanvas.assetManager = appInstance.assetManager;
there are some new errors now that I'm looking into now, so I'm not certain if this patch was correct