I had this problem just one minute ago. Clean up the cache worked for me:
app/console cache:clear --env=prod
Hope this helps.
If clearing the cache or dumping the assets doesn't work. Try noisebleed's comment:
// app/config_dev.ymlassetic: use_controller: true bundles: ['FooBarBundle']
Maybe you have removed the assetic routing from the app/routing_dev.yml
_assetic: resource: . type: assetic