This is not an issue, as per pega when some action is performed on the workobject and if same workobject needs another action need to wait till first action completes thats whey they introduced locking concept.

The lock cen be Default or opthimistic 

Hello,

I think this is a classic situation where you have an assignment on a list but the assignment has been processed already by an SLA or another user.

But your screen hasn't been refreshed and you think you still have this assignment available. So if you click it to process, you get this message.