The tasks in my workflow are created properly by K2 in the SharePoint task list, an email is properly sent, the task is created in the list, and they can be actioned, but they randomly do not update and so they perpetually show "Not Started". The next tasks are created, and the workflow moves on. In fact the item can eventually be approved, but random tasks or sometimes all of them in the workflow never change the Outcome so the workflow never ends.

 I created a new Task list and the results are the same, in the K2 Workspace no error is reported, it simply isn't updating the Task list from what I can tell. As you can see from the below picture it simply creates the next task after the previous has been actioned, but does not update the list.