hi Jaime,
yeah, pretty much.. you "add" all dependencies of MockServer (like sinon, etc) into your own project and instead of loading from the UI5 resources you load the one in your own namespace.
reason for such is, it would appear there is some sort of issue going on, not on your own code but rather maybe a bug with the UI5 version you're using.. this would remove doubts as you're loading code you control.
probably best to upgrade your UI5 library afterwards so you don't replicate files and versions everywhere - but as a workaround (and to test a solution) it should work.
Cheers,
Dan.