Have not had any problems with mine.....but I have an MBW one. I'll keep an eye on mine.
If someone did step on it to mount....I can see that removing the raised groove and is no longer supporting the bracket. During riding, the vibration may be letting it slide downward past that point. You might need to get anew raised groovewelded onto the swingarm ....they are cast aluminum....just a thought....keep us posted.