Why is my LG L70 dual showing com.android.systemui has stopped working?

A

AC Question

I changed my runtime to ART and it restarted and it came up with a message 'Android is upgrading... Optimizing apps'. when the optimization was complete the scrren got black and there were many pop-up messages like 'google play store is not responding', 'com.android.systemui is not respong' and many more.
How do I get out of this problem without formatting my phone?