It shows 'Unable to show data' compatible issue. I have this problem few a times. One scenario I faced is when I am trying to read data before delivery activity. Though if I continue and try to execute the next activity which is delivery , it got delivered successfully.
Also, few a times, I am unable to see the result of query activity.
I understand that it shows data only when the execution is at that step and to see data in every step, I should enable the option in the workflow properties to keep the result of interim populations between two executions.