Yes, I was able to observe the same. The behavior is different from the old QModal, where everything was rendered when the page was loaded, with the dialog kept hidden, but very much in the DOM. There’s an opportunity for improving the docs (they are really great as they are, but there’s always room for improvement) to explain exactly what gets created when, when can one use refs for fields inside the dialog, etc.
I moved the code for processing the schema and populating the dialog on this.$nextTick right after the dialog is open. Everything works well now.