I get this error once I try to redeploy the app. There doesn't seem to be a way to fix this without erasing the war and exploded directory then it will deploy without error. I find debugging this from looking at the output from the plugin is seriously obtuse. There is nothing printed out about what the server returned. The access logs on tomcat say a 200 success was returned, but nothing else. Just this obtuse exception with no real explanation. I also don't get any errors in the manager logs on tomcat. I feel like there could be a bug here, but because there is no actual error message it's impossible to tell what's really wrong.
Actually I think you are experiencing the same thing. Notice this line:
projs.war is not deployed. Doing a fresh deployment.
I'm not sure why the plugin can't undeploy or redeploy, but it's not working. I've checked my logs and stopping the app should work, but I don't see it trying to stop it.