Unknown column ” in ‘where clause’

I am trying to search for related products within the admin page of a product. No results are shown and i get the following error in my nginx error log.

I am using mysql 8 / php 7.4-fpm and the current version of WordPress (5.6) and WooCommerce (4.8.0).

Any ideas? :/

IMAGE: https://i.stack.imgur.com/7V2bi.png

2021/01/08 12:05:20 [error] 13624#13624: *256901 FastCGI sent in stderr: "PHP message: WordPress-Datenbank-Fehler Unknown column '' in 'where clause' für Abfrage SELECT DISTINCT posts.ID as product_id, posts.post_parent as parent_id FROM qgwp_posts posts
			 LEFT JOIN qgwp_wc_product_meta_lookup wc_product_meta_lookup ON posts.ID = wc_product_meta_lookup.product_id
			  LEFT JOIN qgwp_wc_product_meta_lookup parent_wc_product_meta_lookup
			 ON posts.post_type = 'product_variation' AND parent_wc_product_meta_lookup.product_id = posts.post_parent 
			WHERE posts.post_type IN ('product','product_variation')
			 AND (  ( ( posts.post_title LIKE '%333%') OR ( posts.post_excerpt LIKE '%333%') OR ( posts.post_content LIKE '%333%' ) OR ( wc_product_meta_lookup.sku LIKE '%333%' )  OR ( wc_product_meta_lookup.sku = "" AND parent_wc_product_meta_lookup.sku LIKE '%333%' ) ))  AND posts.ID NOT IN(9781) 
			 AND posts.post_status IN ('private','publish') 
			
			ORDER BY posts.post_parent ASC, posts.post_title ASC
			 LIMIT 30 
			 von do_action('wp_ajax_woocommerce_json_search_prod" while reading response header from upstream