blog's permalinks not working

That’s actually a server configuration issue. All servers should issue a permanent redirect for sneakersbr.com.br/flavio to sneakersbr.com.br/flavio/ .

You should definitely contact your hosting provider.

what exactly should I tell them?

Just describe the issue in detail. Something like this:

Hello, I’m having an issue with my site.

sneakersbr.com.br/flavio is returning a 404 (not found) error while sneakersbr.com.br/flavio/ is working properly.

I’ve been told that this is a server configurations issue and that sneakersbr.com.br/flavio should be issues a 301 (permanent) redirect to sneakersbr.com.br/flavio/ .

Thank you for your assistance!

Will do.
Thank you, James.

You’re welcome!

I just noticed that this isn’t related to the server config. Because that are some blogs that sometimes it works and sometimes it gives me a 404. Even with the trailing slash. Other thing I noticed is if it’s a page related to the main site it works with or without the ‘/’. But if it’s a blog (or sub site if you will) it doesn’t.

Very weird.

Now it’s happening even with the main site. I try to access some /category/ (or /category) and it gives me 404. And if I reload few times it brings me the right page.

What do you have entered for the two URLs at Settings/General in your Dashboard and your permalink structure at Settings/Permalinks?

for the main site is: /%category%/%postname%/
and for the others: /%year%/%monthnum%/%day%/%postname%/

Ok, that looks good. How about the two URLs at Settings/General in your Dashboard?