I've had this issue on four different trailers over the years and only one of them was down to the damper. Easy to check...Pull the handbrake on hard and try pushing in the ball hitch, it should be do-able (just) or put a ratchet strap round it to pull it in release the handbrake then the strap and it should "creep" out.
Three of the trailers (one car transporter and two boat trailers) all had the same issue with the handbrake pivot rusted and seized to the overrun lever. This makes adjusting the brakes futile because the hitch mechanism is in an "already deployed" state and there is not enough travel left in it for the brakes to work. This sounds much more complicated than it is but basically the lever that operates the link rod/wire for your brakes should move independently of the handbrake (apart from when you apply the handbrake).
