How to reproduce:
1. Open the attached project and "Repro" scene
2. Open Timeline window and select "A" GameObject in Hierachy, notice that it has Control Track with "B" GameObject assigned as its Source Game Object
3. Select "B" GameObject in Hierachy with the Timeline window opened
4. Right click on the Control Track and add Control Playable Asset Clip
5. With the Clip selected, drag and drop "A" GameObject from Hierarchy to a Source Game Object property

Result: Crash most of the time occurs on:

========== OUTPUTING STACK TRACE ==================

0x00000001404FF24F (Unity) RecursivePlayableTraverser::Traverse
0x00000001404FF34C (Unity) RecursivePlayableTraverser::Traverse
0x00000001404FF34C (Unity) RecursivePlayableTraverser::Traverse
0x00000001404FF34C (Unity) RecursivePlayableTraverser::Traverse
0x00000001404FF8E5 (Unity) PlayableOutput::PrepareTraverse
0x00000001404FFFA6 (Unity) PlayableGraph::PrepareFrame
0x00000001405022C4 (Unity) PlayableGraph::Evaluate
0x0000000141850511 (Unity) PlayableDirector::Evaluate

Reproducible with - 2017.3.0a7, 2017.2.0b11, 2017.1.1p1, 2017.1.0b1

Note: Crash also occurs on HPlayable::IsValid (mostly 2017.2), Playable::PrepareFrameVisitor (2017.1)