Sounds like some of these mirrors require the user to concentrate or position their head just right in order to see.
If I were to go back to using a mirror, I would use the "Italian Road Bike Mirror" (IRBM) as it has crystal clear image and unmatched FOV for it's size. No vibrations and it stays in place once mounted. Although there are other brands that look like "Italian Road Bike Mirror"....do not make the mistake by thinking the ones that look the same are the same. The IRBM is in another league and similar mirrors by other brands are junk in comparison. The catch is it is not adjustable after you mount it. It is mounted and positioned based on your position that you spend the most time in on your bike (ie. drops or hoods). Now you can still see in either position, but the image is optimized based on the position you set it for (drops or hoods).