We have used a cockpit cover (the grey thing you see above) on the Miata for 15 years now. Not all the same cover, there have been several since the first in 2002. After awhile the car cover fabric that they are made of deteriorates due to sun exposure, and continually being folded and tucked into the side of the trunk, so they need replacing every now and then. The one above is a hold over from The Emperor and is only a couple years old, so it probably still has a couple more years left.
Do you see that black strap hanging down by the front of the door? It has a felt covered hook that is supposed to be hooked into the edge of the wheel well (sort of like the strap on the back.) These straps have a tendency to fall off like this if the cover doesn’t get hooked around the mirrors just so. I’ve tried adjusting them longer or shorter and re-positioned in the wheel well to no avail. Invariably, even though the seem solid when put on in the morning, one or the other will be dangling uselessly by lunch or quitting time.
Today both of them were just hanging by mid-day. This is the straw that broke the camel’s back. I am going to cut them off. They really aren’t needed because the front of the cover gets tucked under the windshield wipers. I’m thinking if the wind is strong enough that it can get under the cover with the wiper arms holding it down and lift it up, it then has to break the velcro bonds around both mirrors to make it flap off. And if this is the case it is way too windy to be using the cover in the first place.