I sympathize with you... I'm at a plateau too.
I have heard that over an hour of cardio exercise, you can lose muscle... but maybe what you need is an exercise "shake-up". Maybe try a different routine, different intervals, different inclines.
I didn't read about how much resistance training you do. Maybe a change is needed there as well. Like some plyometrics, compound exercises, maybe some walking lunges or step-ups with weights.
I'm beginning a new routine tomorrow. It's a diet and exercise "shake-up" for myself!
I wish you the best!! Don't give up!
