I would take the wheels off and carefully examine your tyres. I’ve had mine standing for a while the rears were due as worn but the fronts have plenty of tread only about 6K on them but were loosing air. I only noticed why when I had the wheels off the rubber had small splits all around the circumference in between the treads and are a potential disaster. I have not got a clue what’s caused the tyres to deteriorate like that.