When reading from UART and trying to write the read line to a file the board has a hard hang. I've confirmed the following code causes the issue on both an RPI Pico and a Pimorini Pico Lipo. The hang occurs anywhere from the first iteration of the loop, most often early, but can run to 10 or 20.

*Note: I'm not sure if this is the same issue as (https://github.com/micropython/micropython/issues/7204) but thought I'd raise anyway.

I've run the same code on an ESP-32 board (Firebeetle v4) with no issue. The UART is read and line written to file with no issues.

Sample code that draws the error (apologies I'm not the best coder so apologies for the quality of the code):
import os
import machine

#print sys info
print(os.uname())

f_debug = open('debug_test116.log', 'a')
f_debug.write('=======STARTED =======\n')
f_debug.flush()

#print uart info
uart = machine.UART(1, baudrate=9600, txbuf=1024, rxbuf=1024, timeout=1000, timeout_char=4 )
print(uart)

i = 0
while i < 1000:
line = uart.readline()
f_debug.write(str(line))
f_debug.flush()
print(line)
i = i + 1

print()
print("- bye -")