Page titles appear too big and, oddly, in a big red rectangle. I added a plugin to hide page titles. It worked out, but now when I open a page the red rectangle appears for a second and disappears.
I would like to get rid of this odd thing all together.
I visited your shared site and it seems this is happening because of tablepress plugin that you are using on your site so to confirm it please try temporary deactivating tablepress plugin and see whether everything works fine.
If you want to remove this page title then you can try achieving this by adding the following CSS code in the Custom CSS option of your theme on the below path.
Admin Area -> Appearance -> Unite Options -> Other -> Custom CSS
As you said, it was the Tablepress which was causing all this mess, but deactivating it would kill my established tables. So I opened the plugin options and disabled the “Custom CSS” there. It worked!