Updating Failed, ver 3.8

Hello,
This is a site that I transferred from another domain. I used wp migrate db to change the domain name and zipped the files and then extracted on new server. I do this ALL the time and have never had an issue.

I decided to install Gutenberg on the site to see how it would do. Unfortunately when editing Posts (only posts, pages are fine) when I click update I get “Update Failed”.

Console shows this error:
POST https://tcwprintshop.com/wp-json/wp/v2/posts/1326 403 ()

Network shows similar 403 error:
1326 | 403 | fetch | index.js?ver=1536783125:1

I disabled ALL other plugins.
I used the default WordPress Theme.
I deleted and reinstalled Gutenberg.

I contacted Siteground, and they could not figure out the problem and suggested contacting the plugin author. Siteground says they reset all the permissions.

Thank you!