Black screen after upgrade Mojave

[blbwd]

Hello all,

I have just upgraded my Macbook Air to Mojave. After upgrade I am facing a wired situation.

1. I start the laptop
2. Enter the password
3. Now a completely black screen appears for 10 seconds approximately
4. After that the main desktop appears and computer runs fine

I never had such 10 seconds delay with black screen before with previous OS.
Please suggest how to resolve this and what is this issue for.

Regards,
Sanjay