Our Rad Mini ST2 is a week old, and has the same Microshift Mezzo deraileur. The bike will not stay in 6th gear without trying to shift. All other gears are OK, and I've made the adjustments to deraileur per Rad video online. On close inspection it looks like one of the teeth on the guide pulley is bent. Also, inspection of the cassette, (or cogset) shows that several of the teeth are slightly bent out of place. When I unpackaged the bike the chain was not on the front sprocket, but resting on the inside of it, by the frame. Not sure if this little bit of torque on the cassette could have bent the teeth, but I guess it is possible. In either case, I will be contacting RPB today to try and get resolution, and express my disappointment with their choice of substitution parts. I've used Shimano gearing on my bikes for over 50 years, and have never seen anything like this. Will post when I get a resolution.