Reproduction steps:
1. Open the attached project from OC link.
2. Build it.
3. Editor crashes.

#0 0x00000102262d00 in mecanim::animation::DeallocateAvatarOuputForBindings(mecanim::animation::AvatarOutput*, mecanim::memory::Allocator&)
#1 0x0000010154c0b9 in Animator::CreateBindings()
#2 0x00000101541d26 in Animator::CreateObject()
#3 0x00000101540f0c in Animator::Rebind(bool)
#4 0x00000101fc494d in AwakeFromLoadQueue::InvokePersistentManagerAwake(AwakeFromLoadQueue::Item*, unsigned int, AwakeFromLoadMode)
#5 0x00000101fc3d8f in AwakeFromLoadQueue::PersistentManagerAwakeFromLoad()
#6 0x00000101f49a2f in LoadSceneOperation::CompleteAwakeSequence()
...

Note:
Full log in the edit.

Regression introduced in:
5.6.0a3

Not reproducible with:
5.5.1f1, 5.6.0a2

Reproduced with:
5.6.0a3, 5.6.0b5