Error message while executing the test

I created the steps to test a mobile application using the Record Mobile Mode. I executed the test multiple times and it made it through all the steps I created (20 steps), but then when I re-executed the test after adding more steps, it failed at step 2 ( suppose to tap a button ). I am getting this error message:
Root cause: java.lang.illegalArgumentException: Object is null
I haven’t made any change for this step/object: I don’t understand why now it s failing at this step.