Mine was missing on passenger side, when I bought it (one year old). It is very common for the glue under the clip to detach from the channel surface. Luckily I got a new rubber strip and clip for cheap either from Ebay or Amazon (can't remember ) and then I sealed both driver's and passenger side down with weatherstrip cement. Both sides are on there solid now, lol.
If you are removing yours, and no longer want them, put them for sale, they will go quick, since it is common to lose them while driving on the highway, when the glue bond weakens.