I am on level 219 of Alphabetty saga and the game keeps adding on more required words.
After I have made an 8 letter word (for example - it does it with 6 and 7 letter words too) I get a tick to acknowledge that I have completed that part of the game. Then a couple of moves later, the 8 letter requirement reappears and I have to try and make another 8 letter word. It is impossible to complete the level.