It looks like you’re dealing with a GERDA lock where one specific key just spins without retracting the bolts while the others work fine. From the replies here, it sounds like the most common causes are either a slightly damaged key profile or dirt/debris inside the key or lock mechanism. Cleaning the key and the lock barrel carefully can sometimes fix it, and some users also mentioned having a new key cut as a backup option. Since locks and keys need very precise tolerances, even a small imperfection can cause this kind of spinning behavior. Let us know if cleaning helped or what results you got after trying a new key!
