Suction cups often fail with larger temperature changes, also putting it back, well you cant just put a little spit on it, you need to clean the surface properly where it is to go, and the silicone / rubber suction pad too.
In general when i have used suction cup mounts, they come loose every 2-3 months, this even go for my driver side door mounted phone dock ( suction cup part is what came with my Galaxy 2 phone way back in the day )
Of course if you mount on anything but smooth glass it might change and fall off more often, but even that work sort of OK in my car as the sun shade pattern on the top of my windscreen is a pattern with holes in it and not round dots like it is in many other cars.
My car sort of look like that area is made up of the left over of the cars that got the dotted part of the sticker.
Anyway it is easy to feel the uneven surface on my windscreen sun share area in front of the mirror.