w3 total cache Forbidden index

Hello there,
W3 total cache is the only cache plugin which is working for my blog.
I enabled pagecache via disk enhanced.
It works well but sometimes, when users click on the link of the homepage it gets the error: Forbidden 403 You don’t have permission to access /blog/ on this server.
It happens sometimes.
permissions are 755 for pgcache folder and subfolders.
this is my w3 code in .htaccess on root folder

[Code moderated as per the Forum Rules. Please use the pastebin]

p.s. sometimes it happens also that when i click on some posts i get the correct url but the page displayed is another post. It resolves by refreshing