The metal bar of a clamp can be strained by adhesive that drips during gluing operations. Dried glue can also interfere with the ratcheting action of some clamps. To eliminate the problem, use a hacksaw or band saw to cut a roll of wax paper into 2-inch-wide mini-roll. Then, each time you apply a clamp, tear off a strip pf paper to wrap over or under the bar.
And then, different problem - similar solution: