Diagnosis
Poor tumbling. The lifters (the baffles inside the drum) are worn smooth or broken, or you're overloading with heavy items like blankets that just roll instead of tumble.
How to Fix It
First, run a load with smaller, lighter items (like towels) and use the 'Heavy Duty' cycle which has more vigorous tumbling. If the problem disappears, you were overloading. If damp stripes persist, inspect the plastic lifters inside the drum. If they're worn down to nubs, they need replacing to properly agitate the laundry.
If That Didn't Work
An unbalanced load can cause the dryer to shift into 'low tumble' mode to protect itself. Ensure the dryer is level front-to-back and side-to-side using a bubble level on the drum.
Heads Up
Consistently overloading doesn't just dry poorly—it strains the motor, belt, and bearings, leading to premature mechanical failure.