I use FRDM_K64F board and KSDK_1.0.0.
In my program is used UART_4 connected to the RS485, UART_3 connected to the USB and Lwip.
When connected to the network cable after a while stopped taking data UART_4 (RS485).
The program is part of the interrupt handler, but the function UART_HAL_GetRxDataRegFullIntCmd (baseAddr) is always false.
Thus UART is connected to the USB works correctly.