Steps to replicate the issue (include links if applicable):

I made a Google Doc with reproducible steps, you can see (and use it to copy/paste) here: https://docs.google.com/document/d/1nU2rYurrkOQ9HhEmJW_rEwXpDjPxmJIwVwoYkefJEHM/edit#heading=h.whecslmaf5g3 (Problem #1)

The steps are:

• Create a Google Doc with headings
• Make the headings "numbered" in the Google Doc
• Copy the entire document (or even just the heading) to VisualEditor page

What happens?:
Visually, nothing, which was odd. The console has an error:

Uncaught Error: Cannot insert mwHeading even after closing all containing nodes (at index 2)

What should have happened instead?:
Either strip the numbering, or translate the numbering to a preceding number (1. xxxx) ?
Either way, this should at least not fail, and give some indicator to the user that something was off with the original text.