M2s and M3s wheel mechanism is different from M3.
To give everybody more details regarding wheel falling off:
Wheel is hold inside player by plastic parts, no glue, not relying just on friction. Onto wheel we attach plastic ring, that holds on to it by two tiny plastic legs. This plastic ring is then attached to the body of player by three plastic legs.
Here I took one photo to show you in detail.
You can actually detach wheel from the player if you wish, I do it simply by putting my nail under edge of wheel and pushing away from the player until it pop off. Then to put it back, just align the sprout of wheel with hole inside player and pop it back into place.
Here is photo of wheel I just took of from my M2s.
So if your wheel fall off from the player, it could be caused by accidentally somehow applying force in the one correct direction. Then you should be able to just pick a wheel, pop it back into place and be all good.
In some cases, maybe the ring got damaged and one of the tiny plastic legs got broken. In that situation, you can contact us and we will gladly send you one wheel to replace it on your unit. We will also send some spare wheels and plastic rings to our distributors, so they can provide it to you too.
If you have any more questions, just directly ask me. I spend today running around our technicians, getting all the detailed info on the wheel, its mechanism and the problems we are facing, so can provide you with any details you need.