Reproduction steps:
1. Open the attached project "Mechanim Bug.zip";
2. Open the scene 'Test Scene' and hit play. There are 3 cubes, each of them has a different animator culling mode;
3. Click the on the button "Disable Objects" to make each cube inactive in the scene;
4. Select "Pause Time" to set the timescale to zero;
5. Click the button "Enable Objects" to have the cubes set to active again (while the timescale is zero);
6. Click on the "Start Time" button to set the timescale back to 1.

Expected results: After enabling Time again, all three cubes should be animated again.
Actual results: The red cube (set to culling mode 'CullCompletely') is not animated.

Reproduced on: 5.6.0f1, 5.6.3p2, 2017.1.1f1, 2017.2.010, 2017.3.0a7.

Note: Not able to reproduce the issue on lower than mentioned versions as some of the used methods including "fixedUnscaledTime", "inFixedTimeStep" and others, were introduced only on 5.6.0f1.