Java fern and anubias typically come from emersed farms (see pictures below), actually most aquarium plants come from emersed farms, meaning they are grown outside of water. Why? Because growing emersed is quicker, cheaper, and you don't need to worry about algae. Whenever you transition them to fully submerged, it's important to make it as easy as possible for them to transition by providing CO2 through pressurized injection/diffusers. As they are used to an a near infinite amount of it and are now limited to 2-5 ppm found naturally through normal gas exchange, the plants will be stressed out and may lose some leafs before new growth that is accustomed to the new environment may appear.
(You may lose no leaves in the case of java ferns or anubias, but in the case of other plants there are emersed and submerged forms of growth, for example an amazon sword will have oval shaped leaves in its emersed form, and will have sword shaped leaves in its' submerged form)
The frogbit is doing fine and will likely continue to thrive because it has access to atmospheric CO2.
Does this mean you need CO2? Absolutely not, I've grown Java Fern with and without CO2, and its very possible to grow Java Fern without CO2, but the plants don't get as big and aren't as bushy. With CO2 my Java fern grew to nearly a foot tall and was extremely bushy and needed insane amounts of potassium to maintain its biomass.