Obscure Hardware Fault on Pico [solved]

I have got two Picos both bought from you. The first one has a rather odd fault. It is that some PIO program using state machine 0 do not work correctly, but others do. However, using my second Pico state machine 0 works as well as any other state machine number.

The only difference is that the first machine has had C put on it, and then changed back to micro python.
Is this a fault or is there something else I need to do to get state machine 0 to work?
No problem with avoiding state machine zero but it did take me a couple of days to track this down.

By using the flash_nuke.uf2 to erase the flash then all state machine numbers now work again.

Might be of use to someone.