I received an update notice this morning after launching LR6. I downloaded and installed the update. Now when I add new picture folders to My Pictures and tell LR to synchronize...none of the new folders show up!
What is your OS?
There are many confirmed issues with LR 6.2 - you may try the steps here: Update on Lightroom 2015.2 / Lightroom 6.2 Release
Anyhow, you are best helped if you roll back to 6.1.1 as many users: http://www.lightroomqueen.com/how-do-i-roll-back-to-lightroom-2015-1-1-or-lightroom-6-1-1/
My OS is Windows 10
I followed the steps per the link you provided to roll back to 6.11 and that indeed fixed the issues.
Now... how will we all know when Adobe released the "correct" fixed update?
Wait for a the next update like 6.2.1 / 2015.2.1 or 6.3 / 2015.3