OSX El Capitan hangs or freezes during boot or after login acutally

I twice had the case that after upgrading and after an update, my MacBook Pro froze doring / after the login screen.

What didn't help - but what's always worth a try:

• Deleting the NVRAM (Cmd + P + R + Pwr)
• Booting in safe mode (shift + Pwr)

So what was the Problem? Kernel Extensions!  How to fix it?

• Boot into recovery mode (Cmd + R+ Pwr)
• If you have FileVault enabled, open the Disk Utilities, select your main drive (which is grayed out) and select "Unlock..." in the Menu
• Start a terminal
• Remount everything writeable: mount -rw /
• Naviagte to your Kernel Extensions folder: cd /Volumes/System/Library/Extensions
• Look for new or non-standard extensions and move them in a subdirectory called "Unsupported: mkdir Unsupported; mv Stuff.kext Unsupported/
• The list of standard extensions can be found here: ls /Library/Extensions
• Good candidates in my case were Logitech Drivers and or a USB to Serial driver
• Reboot

An excellent writeup of all this can be found here: https://www.justinsilver.com/technology/os-x-el-capitan-10-11-1-hanging-on-boot-fixed/
Note however, that in this tutorial, the step of unlocking FileVault is missing, which is essential when using an encrypted harddisk.