alt_write_flash - single threaded

I'll throw a few ideas your way:

1) Have you allocated enough stack size for each of your tasks? This seems to be likely based on your problem description.

2) Are you making calls to the flash device from multiple tasks? If so, try making the flash calls from a single task only.

3) Is the network stack actively processing when your attempt to make the call to write to flash causes the corruption? If so, what happens when the network stack is idle and you attempt to make the call to write to flash?

4) Are you able to start a task that will write to flash before you start the network stack to see if you can reproduce the problem even before the network stack task is running?

I'll think about this a bit more. Good luck!