I not using the same sensor but a very similar one LD2410 the original one not the "c" version. And really have no idea if this will help or not.
My Uart is configured as below.
uart:
id: uart_bus
tx_pin:
number: GPIO1
rx_pin:
number: GPIO3
baud_rate: 256000
parity: NONE
stop_bits: 1
the first time I set it up on different pins and it did not work. I can only suggest move it to the RX and TX pins.
The config i use came for here
Mine has been working for a few months now, but did take some setting up, to get reliable readings from it.