I am working on an application transferring data from an Arduino (slave) to a Raspberry Pi (master) over an I²C bus. I was in the middle of writing the code, when suddenly the transfer quit working, and I cannot figure out why. I tried re-installing SMBus2, but the problem persists.

Here is some test code, attempting the transfer of 7 bytes from the Arduino:

#! /usr/bin/python3

from smbus2 import SMBus

slaveAddress = 10
blockSize = 7

with SMBus(1) as bus:
    # Read a block of blockSize bytes from address slaveAddres, offset 0
    block = bus.read_i2c_block_data(slaveAddress, 0, blockSize)
    # Returned value is a list of slaveAddress bytes
    print(block)

I have tried several variations, but no matter what I get the following:

[255, 255, 255, 255, 255, 255, 255]

If I issue the command

i2ctransfer -y -v 1 r7@0x0a

I get an expected result of

msg 0: addr 0x0a, read, len 7, buf 0x32 0x01 0x00 0x00 0x00 0x01 0x00

Which means the code on the Arduino and the I²C bus are behaving as expected. What can be wrong and how can I fix it?