I agree with Bagstard. You’re not eating enough and your body is using your muscle mass as well as fat stores to provide your energy.
At the moment you are at slight cross purposes. Cutting back the carbs to lose weight and training for endurance require different things. Effective endurance training requires lots of carbs (as well as protein, good fats, etc) and you should see that amount that TdF riders eat at 4-8% body fat as an extreme example.
At the moment your body will be going into starvation mode, it will lower your metabolism, reduce recovery ability, and actually hinder your weight loss.
Eat more to match your training goals and get your body firing on all cyclinders as a first step. Then alter your diet accordingly so you are in a slight calorie defecit each day after taking exercise into account. 1500-2000 kcals + all that exercise is going to run you down.