I Had two ZM lenses 25mm and 5cm, I had no problem with either.

But there was detectable rotational play in both of the focus rings, this be easily felt and could just be seen visually. But did not vary in the 3-4 years I had the lenses, I bought them knowing it was there and they were both as new.

When I part exchanged them the dealer has the 25mm serviced cause he could detect the lube was drying out and the friction was uneven. He did not detect the play in the rings.

I sold them cause I found them too big/bulky, they were ok photographically.

The CV M and LTM lenses I have had have not had this or any problems, so I don't think it is build quality, rather Zeiss speciications.