At this point you cannot delete the screen nor edit the screen.
Basically your app is frozen and you can only start a new session which is redundant because it puts your app into the same sitution.
Error Message:
WebAuthoring abnormal termination.
Client date/time: 2017-07-13T13:39:59.617Z
Version: 2.0.661
Session ID: 45ed4f1c-cdc3-b170-242c-1c2f1645f382
description: {"error":{"isTrusted":true,"detail":{"exception":{}},"message":"Uncaught TypeError: Unable to process binding \"if: function (){return !isCustom }\"\nMessage: Unable to process binding \"text: function (){return fieldTypeDisplayName }\"\nMessage: Cannot read property 'length' of null","filename":"https://paaeuscdn.azureedge.net/v2.0.661.0/studio/openSource/modified/winjs/js/base.js?v=39e032536722","lineno":3,"colno":15041,"error":{"detail":{"exception":{}}},"NONE":0,"CAPTURING_PHASE":1,"AT_TARGET":2,"BUBBLING_PHASE":3,"type":"error","target":"[window]","currentTarget":"[window]","eventPhase":2,"bubbles":false,"cancelable":true,"defaultPrevented":false,"composed":false,"timeStamp":105005.36000000002,"srcElement":"[window]","returnValue":true,"cancelBubble":false,"path":["[window]"],"composedPath":"[function]","stopPropagation":"[function]","stopImmediatePropagation":"[function]","preventDefault":"[function]","initEvent":"[function]"},"errorLine":3,"errorCharacter":15041,"errorUrl":"https://paaeuscdn.azureedge.net/v2.0.661.0/studio/openSource/modified/winjs/js/base.js?v=39e032536722","errorMessage":"Uncaught TypeError: Unable to process binding \"if: function (){return !isCustom }\"\nMessage: Unable to process binding \"text: function (){return fieldTypeDisplayName }\"\nMessage: Cannot read property 'length' of null","setPromise":"[function]","exception":{}}
stack: null
errorNumber: 0
errorMessage: Uncaught TypeError: Unable to process binding "if: function (){return !isCustom }"
Message: Unable to process binding "text: function (){return fieldTypeDisplayName }"
Message: Cannot read property 'length' of null
