Im at a loss, i am 50 years old, i do taebo 3x a week, recently started cross fit 2x a week and trail running over weekends. i now seem to gain kgs, why would that be?

Diet: Diet is the major possible cause. Watch calories and limit carbohydrates. If weight gain persists, speak with your doctor about lab tests to look for other possible causes of weight gain

The basics: Exercise triggers appetite and lots of exercise triggers increased muscle density which is heavier than fat. You win the battle over weight at the dinner table, not on a treadmill. A slice of pie equates to an hour of exercise. If you reward yourself with food you will always gain. A consultation with a clinical nutritionist can give you incite on what your needs are and how to avoid weight gain.