Why are tests restarting in Github?

[tcak via Digitalmars-d]

There are 10 test. Some of them gets completed. And then, I look 
at it again, tests have restarted, and less number of tests are 
passed at that point.

1. What is the reason of restarts?
2. What is reason of long waiting time? Sometimes number of 
passed tests stay there 2-3 days.