AH01797: client denied by server configuration error

Hi, I’m constantly getting an error in my error log for months. It’s says (a sample row)

[Wed Jul 19 13:22:05.917359 2017] [access_compat:error] [pid 5438:tid 139922657863424] [client 109.xx.xx.xxx:22145] AH01797: client denied by server configuration: /home/xxxx/public_html/wp-content/plugins/yith-woocommerce-zoom-magnifier/assets/css/index.php, referer: https://xxxxx.xx/wp-content/plugins/yith-woocommerce-zoom-magnifier/assets/css/yith_magnifier.css?ver=4.8

The front side is ok, but why do I keep getting that error?