array_intersect_key(): Argument #1 is not an array, model.php:400

I’m getting a PHP warning persistently – on the front-end on a single post page, in the admin posts list and edit screens.

This is part of a multisite install, the plugin is network-activated. Other networks with nearly identical configurations aren’t having this problem.

I’m on the latest version of WP and Polylang.

The warning isn’t breaking things (that I can tell), but I’d like to resolve.

the warning is:
array_intersect_key(): Argument #1 is not an array

location:
/home/brock/public_html/wp-content/plugins/polylang/include/model.php:400

call stack (edit view):
csp_php_error_handler()
array_intersect_key()
PLL_Model->get_translations()
PLL_Model->get_translation()
PLL_Admin_Filters_Post->post_language()
do_meta_boxes()

call stack (admin list view):
csp_php_error_handler()
array_intersect_key()
PLL_Model->get_translations()
PLL_Model->get_translation()
PLL_Model->get_post()
PLL_Admin_Filters_Columns->post_column()
do_action(‘manage_post_posts_custom_column’)
WP_Posts_List_Table->column_default()
WP_List_Table->single_row_columns()
WP_Posts_List_Table->single_row()
WP_Posts_List_Table->_display_rows()
WP_Posts_List_Table->display_rows()
WP_List_Table->display_rows_or_placeholder()
WP_List_Table->display()

https://ww.wp.xz.cn/plugins/polylang/