Not really sure what it means but definitely Pro RC3 related:
- Installed a completely fresh install of WP 5.6
- Immediately Installed Pro RC3
- Went to add my first page and this flashes on screen for an unreadable second before taking me to WP page creation.
- Deactivated RC3 and warning went away.
Warning: array_intersect_key(): Expected parameter 1 to be an array, string given in /home/redacted/redacted/wp-includes/rest-api/class-wp-rest-server.php on line 1402
Warning: Cannot modify header information headers already sent by (output started at /home/redacted/redacted/wp-includes/rest-api/class-wp-rest-server.php:1402) in /home/redacted/redacted/wp-admin/admin-header.php on line 9.
Update: and perhaps related – once on the WP page creation screen there is no Edit with Pro ability.