Are the stored styles for effects the right ones in factory presets? If you recall a factory preset, go into an effect menu, change the style, then set back the same style, the sound can be different why? Do you have hidden styles?
What happens with the factory bank is that the styles have been modified by us to make unique presets, so it's not exactly a missing style, it's just saved in the preset with tweaked parameters.
If you like the sound of an effect block in a factory preset, copy it into a favorite, then edit any other parameter except the style.