CV drop ?

Probably because Sonic Generations bug.

https://www.steamgifts.com/giveaway/qoSeO/sonic-generations-collection
Now $0

Hit me as well

Isn't "A New Beginning" one of those games like deponia?
During sales it's value rises ten times because it's in some package? And after sale ends it come back to normal value. (just guessing - don't know for sure).

Some price could drop in steam store or some games could be added to bundle list - many possible reasons for cv drop :)
Edit - looks like guys above found real answer xD

It seems that it won't be fixed unless cg builds a better mechanism. If something is removed from the store, you will get no cv.