Welcome to the community forum.
You can boot the phone in safe mode to get a hint whether Apps might be the problem … https://support.fairphone.com/hc/en-us/articles/217869383.
A factory reset in the Android world only deletes user data and Apps and doesn’t touch the OS.
If a factory reset doesn’t help, you can go one step further and reinstall the OS from scratch … 🇬🇧 🇩🇪 ✏ Installing the Fairphone 2 from scratch in case of failure / Komplette Neuinstallation des Fairphone 2 im Fehlerfall.