Usaully a bit of movement in that part of cable into bulkhead,have you checked the cable hasn't melted near to manifold????

Could be a few things though,does ratchet on the peddle make any noises when you get the problem,clicking or slipping etc????

If alls well with cable/ratchet/peddle take the cable off the clutch release arm and try moving cable back and too to see if it travels freely

Could be something wrong with the clutch then,release bearing dodgy etc