To reproduce:
1. Create a new project
2. Create an empty game object
3. Add Network Manager and Network Manager HUD components to it
4. Open Activity monitor if on MacOS, Task Manager on Windows
5. Build for standalone
6. Open the built project
7. Press Server only
8. Observe as the CPU usage goes to 40 - 60 %

Expected result: CPU usage is a bit bigger than on idle or the same
Actual result: CPU usage goes to 40 - 60%

Reproduced on:
2017.3.2f1 2017.4.6f1 2018.1.5f1 2018.2.0b9 2018.3.0a2

Notes:
Works fine on: Intel(R) Core(TM) i5-7600 CPU @ 3.50GHz Windows machine
Reproduced on: MacOS 10.13.5 Intel 3,4 GHz Intel Core i5