In my app I use a Google Maps package. When adding an info view (those little popups over a marker) with a custom node element Velocity seems to break everything somehow. When removing Velocity everything runs fine. What is wrong with Velocity? It is really sad that testing in meteor is so troublesome 
Here is what I do:
let div = document.createElement("div");
new google.maps.InfoWindow({content: div});
And here the error:
velocity_source-map-support.js:90 Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user’s experience. For more help, check http://xhr.spec.whatwg.org/.
velocity_source-map-support.js:90 XMLHttpRequest cannot load https://maps.googleapis.com/maps/api/js?v=3.exp&language=de&callback=GoogleMaps.initialize. No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘http://localhost:3000’ is therefore not allowed access.d @ velocity_source-map-support.js:90l @ velocity_source-map-support.js:91b @ velocity_source-map-support.js:94(anonymous function) @ velocity_source-map-support.js:95z @ velocity_source-map-support.js:95vb @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:36_.wb @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:37(anonymous function) @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:40(anonymous function) @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:40(anonymous function) @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:40(anonymous function) @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:41_.m.setValues @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:89_.be @ js?v=3.exp&language=de&callback=GoogleMaps.initialize:63(anonymous function) @ VM4456:2InjectedScript._evaluateOn @ VM4453:875InjectedScript._evaluateAndWrap @ VM4453:808InjectedScript.evaluate @ VM4453:664
velocity_source-map-support.js:90 XMLHttpRequest cannot load https://maps.googleapis.com/maps/api/js?v=3.exp&language=de&callback=GoogleMaps.initialize. No ‘Access-Control-Allow-Origin’ header is present on the requested resource. Origin ‘http://localhost:3000’ is therefore not allowed access.d @ velocity_source-map-support.js:90l @ velocity_source-map-support.js:91b @ velocity_source-map-support.js:94(anonymous function) @ velocity_source-map-support.js:95z @ velocity_source-map-support.js:95InjectedScript._describe @ VM4453:1117InjectedScript.RemoteObject @ VM4453:1202InjectedScript._wrapObject @ VM4453:368InjectedScript._createThrownValue @ VM4453:826InjectedScript._evaluateAndWrap @ VM4453:814InjectedScript.evaluate @ VM4453:664
js?v=3.exp&language=de&callback=GoogleMaps.initialize:37 Uncaught DOMException