Just for reference, if someone finds this thread in the future, the reason of the issue was not the mixup of the LPUARTx registers, but incorrect values of the LPUART3_TX_SELECT_INPUT and LPUART4_TX_SELECT_INPUT DAISY registers that my library was setting during init.
The reference manual annotations however still need correction as mentioned here. Hope @PaulStoffregen will be able to do it in the next revision.
The reference manual annotations however still need correction as mentioned here. Hope @PaulStoffregen will be able to do it in the next revision.