This sounds really frustrating. Can you provide a clone to an app replicating the simplest ‘Form1’ issue you describe?
What happens when you try the Page Break demo in the Anvil Extras Demo app (which you can also clone and play with)? It worked for me when I tried just now.
You could also try cloning the tutorial app and try running that: Generating PDFs with Python
I don’t see anything glaring in a quick review of your code, but I’m also not super experienced with PDF generation. Seeing whether the above pre-existing apps successfully generate PDFs for you may help narrow down the issue.