field_attach_update stopped working - how to debug this?
You can't debug what ain't a bug :)

status is a property, not a field, of the commerce_order entity type - so it isn't affected by running field_attach_update(), which just saves field data, and avoids saving the entity itself.

You'll need to use commerce_order_save(), entity_save(), or manipulate the commerce_order table directly, and then clear the cache using the entity controller.