Do you have custom htaccess rules or htaccess files placed anywhere within your WordPressinstallation? , other then the one generated by WordPress. If only the one generated, have you added anything to it?
If you don’t know what that means, it’s likely a “no”..
Files should be 644, but 755 won’t prevent them working.. it just means the permissions are higher then they need be..
Ideally, you should fix the permissions(too high permissions can make your site easier to compromise). However let’s stick to one problem at a time…
Looking back, i think my previous statement regarding your uploads path working could have been wrong..
Can you visit yoursite/wp-admin/options.php , there’s no link for it in the admin (it’s not something user’s need to typically see), so you’ll have to update the URL in your address bar.. This will give you a long list of options and their values, can you check what the uploads path reads on this page please.