I got this error when trying to save a post on the frontend:
[28-Dec-2021 02:27:20 UTC] PHP Fatal error: Uncaught Error: Cannot use object of type WP_Error as array in /htdocs/wp-content/plugins/meta-box/inc/fields/taxonomy.php:219
Stack trace:
#0 /htdocs/wp-content/plugins/meta-box/inc/fields/taxonomy.php(180): RWMB_Taxonomy_Field::add_term()
#1 /htdocs/wp-content/plugins/meta-box/inc/field.php(576): RWMB_Taxonomy_Field::value()
#2 /htdocs/wp-content/plugins/meta-box/inc/field.php(247): RWMB_Field::call()
#3 /htdocs/wp-content/plugins/meta-box/inc/meta-box.php(307): RWMB_Field::process_value()
#4 [internal function]: RW_Meta_Box->save_field()
#5 /htdocs/wp-content/plugins/meta-box/inc/meta-box.php(290): array_map()
#6 /htdocs/wp-includes/class-wp-hook.php(305): RW_Meta_Box->save_post()
#7 /htdocs/wp-includes/class-wp-hook.php(327): WP_Hook->apply_filters()
#8 /htdocs/wp-includes/plugin.php(470): WP_Hook->do_action()
#9 /var/w in /htdocs/wp-content/plugins/meta-box/inc/fields/taxonomy.php on line 219
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