Strange messages in Apache log

In my Apache log I have messages like this:

[core:crit] (13)Permission denied: AH00529: /var/www/vhosts/example.com/httpdocs/wp-content/plugins/wooswipe/pswp/default-skin/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable and that '/var/www/vhosts/example.com/httpdocs/wp-content/plugins/wooswipe/pswp/default-skin/' is executable, referer: https://www.example.com/wp-content/cache/autoptimize/css/autoptimize_5544caf83502c8f989c0003d83f9640a.css

I posted here because of the referer but I’m not sure it’s something related to Autoptimize. Someone is able to explain what is going on? ?? Thanks for any input.