Night time skybox glitch

So, I have played a lot of Black Mesa but each time I get to the outside area of On a Rail, or a multiplayer map that is night based, I see that really cool realistic effect on the stars that makes them blink but, after some time, they just stop blinking and are only doing it when I the player move its kind of upsetting.

Founded in 2004, Leakfree.org became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.