I just tried the tutorial and I was not able to reproduce your error.
I notice you have a "travel" node in your pages app, whjich should not cause trouble... but I guess you did ssomething different then follow the tutorial exactly? Maybe try again from scratch?
I used 6.2.19 as well.
You use the impoort action - does the problem happen when you add the file to the dialog.... or only once you try to save the dialog?
If you are with a parter or DXCore/Enterprise customer, then I would recommend opening a support ticket so that you can get more dedicated assistance.