Candidly, you may be looking at hardware failure of the camera. To further rule out potential software issues:
Please clear both the app and, if applicable, the Android system caches: How to Clear Cache on Android – Republic Help. If after these steps normal operation is restored, you’re done.
If clearing the cache(s) doesn’t sort things the next step is safe mode: Safe Mode – Republic Help. Safe mode is intended to be a diagnostic tool not a permanent solution. If your phone behaves better while in safe mode, there is a third party app at the root of the issue. You’ll need to identify and remove that app.
If all else fails, it’s time to factory reset your phone: How to Factory Reset a Cell Phone – Republic Help. Please know a factory reset removes all user content stored on your phone. Presuming your phone is stable enough to do so, please note Republic’s guidance for backing up that content prior to proceeding with the factory reset.