I was excited about the latest 1.9.1 update,
but I can’t build with it and Unity 2018.3 or later.
The reason is that these following classes have references to UnityEditor,
so these references should be surrounded by #if UNITY_EDITOR directives, but not.
Indeed, I can confirm that this is a mistake I did.
Using #if UNITY_2018_3_OR_NEWER && UNITY_EDITOR is the correct fix.
The CutsceneGroup.cs unfo related calls, are already wrapped in UNITY_EDITOR by the way (all Add and Delete methods are in fact).
I have also attached for you here a fix related to build regarding rotations bug in UnityObjectUtility.cs for your convenience.
I will update the package shorty with the fix.
Thank you! 🙂