We are showing the same exact issue.
Exact same issue for me too, and disabling either Gutenberg or Classic Editor brought the Yoast SEO metabox functionality back.
Errors on Chrome:
analysis-791.min.js?ver=7.9.1:1 Uncaught ReferenceError: yoastWebpackJsonp is not defined
at analysis-791.min.js?ver=7.9.1:1
wp-seo-replacevar-plugin-791.min.js?ver=7.9.1:1 Uncaught ReferenceError: yoastWebpackJsonp is not defined
at wp-seo-replacevar-plugin-791.min.js?ver=7.9.1:1
I enabled Gutenberg, didn’t like it, went back to classic editor and noticed Yoast block was there, but none of the content / tools. Disabled Gutenberg plugin and Yoast started working like normal.
Same issue, disabling Gutenberg solves the issue for now.
I think I’ve found the issue.
In the file /wordpress-seo/admin/class-admin-asset-manager.php on line 178 is the function scripts_to_be_registered there is a check on line 196 for Gutenberg.
It is checking for Gutenberg based on if a function used to enqueue Gutenberg scripts exists, which as long as it’s enabled will exist.
It seems like there needs to either be a hook added for us to make use of or for check for the Classic Editor plugin and if Gutenberg is disabled or not to be added.
The issue can be temporarily fixed by just adding “&& false” to the if statement on line 196. Hopefully a patch is added in the next version of Yoast.
Based on the information you provided, we expect this to be a bug.
We’re actively using the bug tracking on our GitHub repository so your best next step would be to create a new issue for our developers at https://github.com/Yoast/wordpress-seo/issues/new. You will need an account to create a new issue. If this is your first bug report, please check out: https://kb.yoast.com/kb/how-to-write-a-good-bug-report/.
Don’t forget to include the URL to this conversation in your bug report.
This has been fixed in version 8.0 — there is now a function that checks for both Gutenberg and the Classic Editor plugin: should_load_gutenberg_assets().
Thanks guys