I have been experiencing this problem with Gutenberg for a couple of months, so I thought I better report it. This problem happens with Chrome on the latest MacOS as well as on iOS 12.0.1
I paste formatted text that I created in Evernote. I paste it into a block. I have to reinsert carriage returns between paragraphs. When I do this, the Gutenberg editor repositions to the bottom of the page so that I have to scroll back up to the insertion point.
Also with 4.9.8 there is another bug. If I have characters that are bold or bold-italicized, then the space after them is deleted. So I have to reinsert the space.
A possible 3rd bug is that when I paste text of various sizes, they are all converted to one size. Maybe that’s intentional?
This video demonstrates the first 2 problems as well as how to post appears in preview.