The magnets can't seal if the vent path isn't straight. Your dryer exhaust and wall exit must be aligned within 1-2 inches. If they're misaligned, the magnets will separate under vibration.
Unplug the dryer. Check the alignment. Reposition the dryer or wall assembly if needed. Secure the hose with the supplied clamps at both ends. Push the dryer back; the magnets should self-align and seal. A proper seal is critical for lint and exhaust flow.