How to reproduce:
1. Create a timeline playable asset.
2. Create a new scene and add a new Playable Director referencing your playable asset.
3. Target & build for any AOT platform.
4. Once deployed onto the AOT platform, observe the console output.

Expected result: No error.
Actual result:

ExecutionEngineException: Attempting to JIT compile method 'System.Collections.Generic.List`1<UnityEngine.IntervalTree`1/Entry<UnityEngine.Timeline.RuntimeElement>>:.ctor ()' while running with --aot-only. at UnityEngine.IntervalTree`1[UnityEngine.Timeline.RuntimeElement]..ctor () [0x00000] in <filename unknown>:0 at UnityEngine.Timeline.TimelinePlayable..ctor () [0x00000] in <filename unknown>:0 at (wrapper managed-to-native)
...
PlayableAsset returned a null Playable on Instantiate (Filename: C:\buildslave\unity\build\Modules/Director/PlayableDirector.cpp Line: 346)

Regression first introduced in - 2018.3.1f1
Reproducible with - 2018.3.2f1