only thing I can complain is the time consuming needed to lvl up all 52 creatures, they have now this new creature management system that help a lot when your creatures are maxed out, but before that it is still slow to lvl them up.
The Dueling Club is a scam, even if you use cheats. The game is literally scripted to make your opponents' effects occur more frequently than yours so that you'll lose more often, which then tricks players into spending more coins on duels (and then spend money on gems when they run out of coins). The spells you learn from the Dueling Club aren't even worth it in the long run, because story/TLSQ duels are stupidly easy even without using cheats. Those spells are only useful in the Dueling Club, so it becomes an entirely self-serving system. As soon as you learn Depulso in year 3, you're all set for story duels for the rest of the game.
if you are using an emulator (like Bluestacks or Nox) close all recently opened apps and a computer restart normally solve the problem (I think its some problem related to emulator memory cache management being somewhat bad after a long time being used without a rest or something, a restart of the PC will clean up that memory and emulator is back to work as it should)
I don't know if this actually happens as well if you are using a real mobile phone or equivalent.