I don’t test on mobile, however, when I click on any date field in my app, a Date GUI appears, and basically stops all data entry on any field underneath the Date GUI. I was able to get around this by not clicking on the date field, but just inserting the date, and then clicking on a textbox or label field above or below the Date GUI. Clicking on the field outside of the Date GUI has the Date GUI disappear. Hope it helps.
Mobile.verifyElementVisible(testObjOfTheDateField)
Mobile.setText(testObjOfTheDateField, '01/01/1980')
Mobile.click(findTestObject('myPage/input_Basic.LastName')) // a field above the Date GUI
Notice no click on the Date GUI.
Edit: I also changed the variable from “…TheDateFiled” to “…TheDateField”