Repro steps:
1. Open user attached project
2. Enter Play Mode and press either one of the buttons in the Game View
3. Observe the messages in the Game View or in the Console

Notice that the time taken for the first Debug.Log message is significantly higher than for the second one

4. Repeat steps 2-3

Notice that now the time for both Debug.Log messages is similar

5. Exit Play Mode, open the LogAfterThreads script and uncomment the Debug.Log statement in the Start method
6. Repeat steps 2-3

Now the pause before the first Debug.Log call doesn’t occur

Reproducible with: 2017.4.18f1, 2018.2.20f1, 2018.3.2f1, 2019.1.0a13