Installations on computer devices degrade, happens all the time.
I would first consider a factory reset, this would take care of user data as well as Apps installed by the user and their data.
If that doesn’t help, a reinstall of the OS would take care of the OS, too … 🇬🇧 🇩🇪 ✏ Installing the Fairphone 2 from scratch in case of failure / Komplette Neuinstallation des Fairphone 2 im Fehlerfall