The OOTB "Lock Payload Process" and "Unlock Payload Process" workflow steps locks/unlocks pages and assets, but Assets do not recognise Lock/Unlock. This allows assets and Content Fragments to be edited while locked. Assets have a Checkout/Checkin functionality instead.
Would you find out for us if Adobe plans to fix this in the near future?
In the meantime, we are creating a custom workflow step for "Checkout/Checkin Assets".