I took a look at chrome. At least on my Mac, if you hit the Chrome button at the top left, there's a drop down to "clear your browsing history". You could try this (it'll remove your passwords too, probably).

But I have a hunch you're running into a new year Amazon glitch and you'll have to wait this out. It be good if someone else publishing a book can chime in. I don't have anything I'm publishing at the moment.

Thanks.

I've been on a 'chat' with Amazon and they say everything is fine their side and it's a browser issue and I should try a different browser. I've had this problem previously, so I don't think it's a new year issue. 

I suggest you save your stored passwords to your computer before you try clearing browsing history.
The instructions to save / export your Chrome passwords on my computer is:
https://support.google.com/chrome/answer/95606?visit_id=638714494162825060-4293446953&p=settings_password&rd=1#zippy=%2Cshow-edit-delete-or-export-saved-passwords

The Steps for exporting saved passwords are:
On your computer, open Chrome.
At the top right, select Profile Profile and then Passwords Passwords.
If you can?t find the Passwords icon, at the top right, select More More and then Passwords and autofill and then Google Password Manager.
Under Export:
On the left, select Settings.
On the right of "Export Passwords," select Download file.
The password list is saved as a spreadsheet file.

I recall I used to be able to bypass the preview, like Timothy's saying, but I'd recheck the manuscript as a precaution in the future if you're able to do that.

You can try deleting your cache and retrying. Just realize many of your passwords are in your browser and you'll have to re-enter them for access. Depending on your system, you can usually do that through your browser settings.

It could be a new year engineering snafu that Amazon's trying to work out. Or maybe, there's a glut of entries right after Jan 1?

Would love to be able to bypass the preview if you can remember how you did it.
I did try using the previewer to check the manuscript but ended up with the same problem. 
I had the same problem trying to make changes on a book quite some time ago and gave up, so I don't think it's a brand new change.
I have had the lost passwords story previously - and I'm on a LOT of websites so deleting the cache would be a last resort. 

Congratulations to your family! Looks like you had a wonderful day.

Normally you can keep going without that completing? Have they changed that?

Alternately, I'd try regenerating the page, and see if it resets or needs to be started again. The process might have hung, so restarting it might work better this time.

On the other hand, they may have changed something on the back end, and it's slowing everything down.

I've tried that a few times over a few days. When I click on 'save and continue' it goes into the generating preview mode - and sticks there.  Emailed KDP but they don't use that email address anymore

Ended up with a 'chat' on KDP. They say it's a browser problem and to try a different browser. Sent me a You Tube link that explains how to get rid of browsing history and cookies. Not comfortable doing that without consulting my technician as I'm likely to stuff up something important. 

I only seem to have Chrome as a browser.