A Unity ID allows you to buy and/or subscribe to Unity products and services, shop in the Asset Store and participate in the Unity community.
Separate names with a comma.
Yes, but my experience is that it a takes a few weeks for them to address issues. I'm blocked at this point, so hoping for answers very soon.
Recently I've been experiencing a lot of crashes and hangs in Unity projects that use XML serialization. OS X El Capitan, Unity 5.4.0 and 5.4.1...
Quick way to reproduce: download "The Courtyard" demo and create a project with 5.4.1f1 on OS X, then try to run the scene.