Yeah at the moment it grows a bit the leafs are growing on top but the roots seem to just be falling off and growing back my guess is on a night its so cold that its making this happenWell it is probably far to cold at the moment even frosty in the mornings so no you can’t expect any tropical plants to thrive at the moment!
I would think you would need some water to grow a floating plant although I am not sure if water lettuce would grow on a wet substrate but it will grow very well outside in a lidded box once the temps go up.