So, I'm having this issue as well. Here is everything relevant I can think of for troubleshooting purposes:
- I'm using the iOS version of the game on an old phone (iPhone 4S).
- Prior to the 2.12.0 update, I'd have to reset the game frequently to avoid crashing mid-battle, but the game was playable. For example, I could do two crypt battles or one campaign/war battle safely before risking a crash on a subsequent battle.
- After the 2.12.0 update, any battle will crash the game for me.
- It's not just battles. Navigating menus is significantly slower since the update.
- I updated to 2.12.1 and still have these issues.
- I have no issues at all on my PC using Android emulator. This tells me the crashes are because I'm using old hardware with limited memory.
Given all of the above, my guess is that something in the 2.12 update is causing the game to consume significantly more memory than it previously did. (Even on BlueStacks on a PC the game stutters more than it used to). Obviously, it's causing major issues for people with older phones. 2.12.1 did nothing to change this.
I hope this information helps whoever might be looking into this.