Is your FP3’s Fairphone OS up to date? (Check Settings > About phone > Build number to find out what version you are on) There was an update earlier this year that was supposed to address an issue like what you describe:
If that doesn’t solve it, you might want to clear cache and storage of the Camera app and Media Storage (a system app) and see if that helps.
Last but not least: What’s the total storage use on your phone? (80%? 90%?)