I am getting an Uncaught ReferenceError: setImmediate is not defined on this line when running under Monix 3.2.0 and Scala-Js 1.0.1. Appears to be a manifestation of this runtime behavior change. Should be able to replace it with:

if (js.typeOf(js.Dynamic.global.setImmediate) != "undefined")

A search reveals no other instances of this same idiom, but it may be worth checking for some of the other breaking changes.