To reproduce:
1. Open Any project
2. In Hierarchy window, create any kind of game object and disable it
3. Open the Animator window and press Create a new Animation
4. In Animation window, after creating animation, click on the animation timeline's numeric scale (top part of the Animation window)

Expected:
Actual:

Reproduced in: 2019.1.0a5, 2019.1.0b6, 2019.2.0a8
Not reproduced in: 2017.4.23f1, 2018.3.8f1, 2019.1.0a4

Stack trace1:

0x00000001419B2EEF (Unity) mecanim::SetValueMask<0>
0x0000000141932D58 (Unity) Animator::ProcessRootMotionStep
0x0000000141932A99 (Unity) Animator::ProcessRootMotionJob
0x0000000141930BA8 (Unity) UnityEngine::Animation::BlockRangeJob<Animator::AnimatorJob>::Job
0x00000001408BAB76 (Unity) JobQueue::Exec
0x00000001408BCB19 (Unity) JobQueue::WaitForJobGroupID
0x00000001408B4C08 (Unity) CompleteFenceInternal
0x00000001419362B6 (Unity) Animator::Sample
0x0000000140CF82FA (Unity) AnimationModeBindings::SamplePlayableGraph
0x00000001422FFD9D (Unity) AnimationMode_CUSTOM_SamplePlayableGraph_Injected

Stack trace2:

0x00007FF673FBACE7 (Unity) mecanim::CreateValueArray
0x00007FF673FAA071 (Unity) mecanim::animation::CreateAnimationNodeState
0x00007FF673F7D073 (Unity) AnimationLayerMixerPlayable::AllocateBindings
0x00007FF673ECA258 (Unity) AnimationPlayable::UpdateInternalStateRecursive<3,0>
0x00007FF673EDC854 (Unity) Animator::Sample
0x00007FF674660EDE (Unity) AnimationModeBindings::SamplePlayableGraph
0x00007FF6756FCB8E (Unity) AnimationMode_CUSTOM_SamplePlayableGraph_Injected