I've tried restarting Steam, reinstalling, nothing so far has worked. Anyone have any ideas how I could fix this? (I've seen for other games changing the Registry can help but I'm not sure what to change.)

Keep game open for 60-80 minutes ( 73 ). If you already had 1000 achievements it will take 1000 seconds to unlock 1001 achievement. Hope you understand this :)

There are 2 achievements that haven't unlocked for me: "Green anaconda" and "Yellow-lipped sea snake" I noticed there are 2 other achievements with the same names that did unlock. Could this be an error where there is supposed to only be 1 instance of these achievements?...

1 or 2? O_o

I am adding more achievements today. Make sure to update the game and unlock them :)