Suggestion for internal links not working on Gutenberg paragraph block (Multisite)

[tezell-mg]

Description

When on a multisite network and in the Gutenberg paragraph block editor the link suggestion feature is not working. It works fine on single site.

Console error:

In case the image is too hard to read on the consol error "GET http://sage-life-site-network.lndo.site/wp-json/wp/v2/search?search=55&per_page=20&type=term&_locale=user" "400 Bad Request"a

Step-by-step reproduction instructions

1. On a site within a multisite network create and publish a page (Page A)
2. Create a second page and on that page (using the Gutenberg paragraph block) add text to that page.
3. Select some of the text and click the Link button.
4. Begin to type the title of the page created in Step 1

Notice that the suggestion functionality does not work. This is the issue.

Screenshots, screen recording, code snippet

Environment info

WordPress Version: 5.7
All Browsers
MacOS 11.1

Pre-checks

• I have searched the existing issues.
• I have tested with all plugins deactivated except Gutenberg.

[getdave]

@anton-vlasenko @spacedmonkey Are either of you familiar with any quirks of multisite which might make the search endpoint of the REST API not work? For example, would we need to pass a blogID when making the request?

[mrfoxtalbot]

@igmoweb, @jconti, do you have any thoughts on what could be causing this feature not to work as expected in multisite? Thank you!

[getdave]

For clarity here is the endpoint being requested in the code

gutenberg/packages/core-data/src/fetch/__experimental-fetch-link-suggestions.js

Line 102 in 9d1d8e3

path: addQueryArgs( '/wp/v2/search', {