I drag and drop a Text widget to a page and I get this.

... so I can't add my text. I click Finish and go back to the Page editor and see this.

After a few minutes I refresh the page again and my Text widget is gone.

I add a new one and this time it's working.

...mostly working, I'm seeing errors again.

Are you seeing anything showing in console?

I haven't looked. Do you mean in Chrome inspector?

Yes, correct.