El Capitan startup screens After installing El Capitan (Currently on 10.11.3), the screen starts with a login prompt, which then displays a progress bar. At about 30%, the screen goes gray, then a faster progress bar completes the process.

I have read several answers and it seems to be related to Filevault.

I did have a GPU problem (MBP early 2011) which I resolved by entering a script available online, where I did modify the boot process disabling the discrete graphics and after that the boot started to display this additional progress bar; since then the motherboard was replaced (Thanks, Apple!), then I deleted all those extra features yet the startup screens remained.  

Is there a way to have just one progress bar for the whole process?

I find that greyscreen somewhat annoying.
There are several ways you can fix this issue. 


Reset NVRAM
Try starting up in Safe Mode
Press and hold the power button for a few seconds until your computer turn off, then release the power button.


Source: Apple Toolbox