after commit for uasyncio streamreader, data read from rs485 always b"". If reverse back, start works like before.
https://github.com/micropython/micropython/commit/db7682e02d3ffd3338f20effc9ad4735a48bf774

for example.

        self.ac_uart = UART(2, baudrate=9600, tx=14, rx=15)
        self.ac_swriter = asyncio.StreamWriter(self.ac_uart, {})
        self.ac_sreader = asyncio.StreamReader(self.ac_uart)

      while True:
            data = await self.ac_sreader.read(-1)
            log.info(f" RAW: {data}")