Get an error in the test version which is not with the normal sencha app watch command

When I run "sencha app build testing" command In Ext js Application . It shows me an error "DOM element with id ext-viewport in Element cache is not the same as element in the DOM. Make sure to clean up Element instances using destroy()" . Here I'm running the index.html,l file which is in Build->testing->ExtUI folder.when I run without the testing one it works perfectly. Can someone help . Ext version 6.6