cdc_com_port_single example loses comms long-term (Jason Watton)

Using the PIC32MZ EFM Starter Kit (PIC32MZ2048EFM144) and Microchip's sample code ONLY... If I run the Microchip example 'cdc_com_port_single' then characters typed are echoed back +1 as expected and the message 'PUSH BUTTON PRESSED' appears if I press SW..