I think what happens is that as you lose weight and ride more the amount of calories you burn from your usual rides decreases. Your body has become more effecient on the bike and you're carring less weight, plus since you weigh less the amount of calories needed to sustain weight is lower. So you need to ride more, ride harder, eat less or all the above to continue seeing weightloss. Basically get back to a calorie deficit.

Also i think i read somewhere, that while losing weight it's very difficult to build alot of muscle so it's probably not realistic to assume that muscle growth is balancing out fat loss. Think this is why bodybuilders bulk up to gain muscle then cut to lose the fat.