This is an input error.
An initial clear will sometimes sort it:

Turn the key to P
Press and hold SUBTOTAL
Whilst continuing to hold SUBTOTAL turn the power off... then back on
Continue to hold SUBTOTAL until the receipt stops printing
Turn the key to R and give it a test.

If the problem continues, you probably have a bad battery and the whole program has been lost. It will need a new battery and programming.

techie
August 2021