From what I have read this an across board issue, and has been reported on a couple of forums now. So pretty much any manufacturer that is using the Bosch Performance and I guess Active line motor could have issues.
I have had personal contact with a Haibike owner that has been suffering with it, and also a Lapierre owner. Sadly the Haibike owner has twice suffered some pretty extensive damage to his bike through it.
It's 100% the small sprocket size that is the issue. None of my previous bikes with a large sprocket size ever suffered from it, and I guess that you only have to look at motocross bikes that have an underside chain tensioner to stop chain suck, to see that a small sprocket causes issues. I have removed my little mod that I made to prevent chain suck, and now that my motor is back in the bike, I'm currently trying a different sprocket and retainer, and will let you know when the results are in.
Another thing that has slowly become a pet hate of mine, is glancing down and seeing a chain that is hardly ever tracking in a straight line, and looking like a banana. No wonder mid drives potentially wear chains so rapidly, when they are having to work across such a wide ratio of gears on a rear cassette. Internally geared rear hubs should really be the way to go for midrive motors.
I also feel that the motors internal gearing is somehow wrong. Even with the smallest front sprocket of 15 teeth, far too much time is spent in the lowest of the rear cassettes first two gears. Many riders, again across brands, are swapping out the rear cassette for a 42 tooth lowest gear. You shouldn't need to be doing that.
I must admit, that I currently really don't have any faith or enthusiasm for this motor.
I know what you mean about muddy clothes. I have to do most of my riding in the evening/night time, and getting back indoors at gone 11.00pm soaking wet and muddy, is not a nice feeling. Roll on dry days and summer.