Please go through STEP 2 in the following post to learn how to see error messages:
ERROR MESSAGE: “Cannot read property ‘destId’ of undefined”
This ERROR message will appear in the JS Console on the node where there is an issue. Keep JS Console OPEN on the side or bottom of your screen while going through your decision tree.
When you see an error message as shown above it means that node in your decision tree does not know what the next node is.
Please check that node and ensure there is no missing connectors.
This should solve this error message most of the time. Otherwise please report issue with your a link to your decision tree and an image of error message.