Photo scan found nothing or missed trips?

The usual causes, in order

1. 1Your camera’s own location setting is off. The most common cause by far, and easy to miss: if the Camera app can’t access location, your photos never get GPS tags in the first place. Check iOS Settings → Privacy & Security → Location Services → Camera — it should be While Using the App with Precise Location on. This fixes future photos; past ones taken without tags stay untagged forever.
2. 2Bounded has limited photo access. With a limited selection, the scan sees only the photos you picked. Grant full access (Settings → Apps → Bounded → Photos) and re-run Re-sync from photos — details in photo access explained.
3. 3The photos aren’t in this library. History from an Android phone, photos living only in Google Photos, or a camera roll you cleared before switching devices — the scan can only read the iOS photo library on (or synced to) this iPhone.
4. 4The photos never had GPS — shots from older cameras, imports, or trips where location was disabled.

Filling what photos can't prove

For stretches with no usable photos, the record is still recoverable: add trips manually (they carry full weight — manual beats automatic), use the calendar’s tap-to-fill for scattered gaps, and keep Smart Tracking on so everything from today forward is captured without photos at all.