Aha - It could very well be that it just doesn’t work in Preview due to technical issues. I’ll check with the Blog dev team and see if they can shed some light.
The await keywords that you are using in the assignPostDataToUIElements function are not necessary. In fact, if the awaited thing is not a Promise, it will nonetheless be wrapped in a Promise, and that Promise is awaited. Theoretically the execution order is changed, but not really such that you’ll notice.
You should just remove the await from all of the statements. You can also delete the superfluous async in the getPost().then() function - it doesn’t do anything.
I’ll let you now what I hear from the devs. 