No idea how this happened. Site was working, installed a plugin last night and uninstalled it.
Admin panel works fine. Whenever I try to edit a page or post, WP throws this error on the live site. I checked from another machine I haven't touched ;) and same error occurs, eliminating the possibility that a Windows 10 MAMP or hosts file configuration could be interfering with php.
The site is running 5.5.3 and php 7.4.1.
The full error:
Fatal error: Uncaught Error: Call to undefined function _wp_array_get() in /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-content/plugins/gutenberg/lib/class-wp-theme-json.php:517 Stack trace: #0 /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-content/plugins/gutenberg/lib/class-wp-theme-json.php(342): WP_Theme_JSON::get_blocks_metadata() #1 /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-content/plugins/gutenberg/lib/class-wp-theme-json-resolver.php(422): WP_Theme_JSON->__construct() #2 /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-content/plugins/gutenberg/lib/global-styles.php(206): WP_Theme_JSON_Resolver::get_merged_data(Array, 'theme') #3 /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-includes/class-wp-hook.php(289): gutenberg_experimental_global_styles_settings(Array) #4 /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-includes/plugin.php(206): WP_Hook->apply_filters(Array, Array) #5 /usr/www/users/rhistory/ridgefieldh in /usr/www/users/rhistory/ridgefieldhistoricalsociety.org/main/wp-content/plugins/gutenberg/lib/class-wp-theme-json.php on line 517
Not sure why the last line's php url is cut off -- any ideas from someone who's been through this before? Total newbie with WP PHP errors and I have to get this site back up by noon _/\_
UPDATE: The problem is resolved by deactivating Gutenberg, which had auto-updated since my last edit on the site.
Gutenberg plugin is mentioned in both the fatal error and stack trace #3, hints at the source of the error.