Check the Environment Library in K2 Management to see what URLs are there, and then a copy of it (Sting table) in the Workflow Server branch. If the URLs there are different, you can try to edit them. You may need to re-deploy your solution in K2. This should also bring the values into alignment, see String Table. 

If these were existing task before the URL change, they may also need to be updated in the Server.worklistheader table, or perhaps a gotoactivity to the same step (if applicable) after the string table have been updated.