I just buyed Volo's Guide to Monsters, but still did not have access to its races in the character builder. Still, the races are accessible from the sourcebook.

Did you buy the full sourcebook or just Compendium only?

The Compendium is the read-only digital version of the book - all you can do is read it. For adding options to tools like the character builder, the full listing needs to be purchased (what you paid for the compendium will be discounted off the full price, don't worry).

I just want to check this as it's a common mistake.

Cyb3rM1nd already pointed out the most likely issue. I’ll just add to it that with the new character sheet, For the past couple of days some things are taking up to a half hour to actually push through to the character creator after purchasing or adding to one’s collection. 

Thank you for your reply! I effectively did buy the complete sourcebook making sure to also buy the ddb content and not the compendium only.