When gliders fail in flight, but pilots manage to land

Good thoughts, thanks.

From what I remember, the most common "loss of a control surface" in flight are usually with glass ships.

-elevator not connected (more common on earlier ships before auto control connect)
-dirty connectors/dry lube in pushrod ball latches or on the ball itself
-failed gap seal safety tape (most common on the top of the elevator, sorta outta sight outta mind) that flips up when flying blanking the control
-a case where a ship was refurbished (2-33?) and cables were run backwards/crossed! Positive control check should make sure it's connected as well as going the anticipated way.

Positive control check helps a lot.
Crude "test" is to move controls quickly while watching them. If it is not connected, inertia may yield a clunk as the pushrod hits the ball. May.
Check safety tapes, replace as needed.
At least in the spring, clean control connect balls with a rag and WD-40 (decent safe solvent), lube the ball and locking mechanism.
After connecting a rod, try to lift it off near the ball. A slow/dirty lock may allow the rod to come off. Just had this a few weeks ago rigging a -21..

Everything you do on the ground, is one more way to avoid an issue in the air.

PS, the closest I have been (that I am aware of) to a control issue was a late day speed pass at home airport. In the pull-up, hit a gust that unlocked the dive brakes (-24) at a bit over 100MPH. Good for me, they didn't bend open, got them closed, cut pattern short, landed fine. Yes, we checked everything out throughly when derigging.