Data was probably entered right after the screen was cleared, and before OMVS had a chance to rewrite the normal screen. Make sure all input data is entered in the usual input area at the bottom of the normal OMVS screen.
If the input data was entered normally, or if this problem occurs and there is no obvious explanation, there may be an error in the terminal or in z/OS UNIX. Follow the usual problem determination procedures for diagnosing and reporting terminal or z/OS UNIX problems.
If the normal OMVS screen is overlaid or blank, you may need to press <PA2> to force OMVS to rewrite the screen before you enter input data.