Diagnosis
The moisture sensors are the two or four metal bars visible inside the drum at the front. If they're coated with fabric softener residue, dryer sheet film, or lint, they can't accurately read moisture. They'll think the clothes are dry when they're not.
How to Fix It
Unplug the dryer. Clean the sensor bars thoroughly. Use a bit of rubbing alcohol on a rough cloth (like a clean dish towel) and scrub the bars until they shine like new metal. Avoid using abrasives like steel wool that could scratch them. This removes the non-conductive film. Also, wipe down the inside of the drum where the bars mount to ensure good contact.
If That Didn't Work
If cleaning doesn't help, try using a different cycle setting. The "Sensor Dry" has different dryness levels (like "More Dry," "Less Dry"). Try "More Dry" or use a timed dry cycle for heavily wet loads like towels. The sensor might be working but calibrated conservatively.
Heads Up
To keep the sensors working, cut down on liquid fabric softener or dryer sheets, which are the main culprits. Using wool dryer balls or a small amount of softener in the wash rinse cycle instead can prevent the gunk from building up again.