Uninstall, clear whatever data is left out of ml, and re install again.
This might help, as it did for me.
Or it might be one of those summer event bug your device is unable to load(which happened to me for whatever reason and it was no longer an issue after a week of the summer event).
Try clearing cache, or doing the above, and if it does not help in any way, then this is a bug for sure.(that happens on some devices)
If this problem still persists, please do click reply on this post and send me your following information:
1. Your Server ID
2. Your Server ID
3. Your device
4. Your current game version.