im using zenfone 3 with android nougat 7.1.1 and had same issues, i think this isnt related to android version and seems to be somenthing related to bad servers of nexon, on original game i had a few problem with connections tooThe same for me, still crashing every battle or if you use instant win after feel times.
If this helps you to found the issue with your mod, here is some info:
My phone is a XIAOMI POCOPHONE F1 with Android 8.1 NO ROOT - Crashing.
On Bluestacks 4 with Android 7.1.2 NO ROOT - For now no issues or crashing.
I don't have much more to share, but for me seems related to the Android version you are using or some memory leak in the mod as I already said the original app or other mods doesn't have this issues.
If you need more info I'm glad to help you.