Today to my great surprise I notices that my Apache web server randomly returns 403 Forbidden HTTP error code to search engine robots. Yandex Search Engine reported that on my favorite website 263 pages are OK and 210 pages has 403 status and some other site has 394/139 pages respectively.
In Apache error logs I found the following messages:
Permission denied: /home/<site-name>/.htaccess pcfg_openfile: unable to check htaccess file, ensure it is readable
as far as I see they appears whenever this 403 error is reported.