My error message says App error 523 I have no idea what happened
I understand how frustrating it is when an error is displayed on the screen of your phone. The error outlined on your post appears to be related to a 3rd party application. Does error display when you open a certain application? If so, please delete that application and re-install as a file may be corrupted and causing such error to display.
If issue happens at random, try uninstalling the last installed applications as one of them must have not installed properly causing the error.