Have you checked the clutch adjustment? Hard to tell from the video what exactly is happening. There different input shafts on T5s. Are you sure the one you have matches the rest of your application? Is it ling enough to fully seat? Seems like it is jumping teeth when you let the clutch out... or something isnt bolted down tight. When I was adjusting the grab point on my T4 if I loosened the pedal travel to much the clutch/throw out arm/bearing assembly would knock pretty bad until I took up the slop in the pedal. Chappy
Clutch issues What engine, bellhousing, clutch, pressure plate, flywheel,clutch fork , clutch pedal, master/slave, cable , pilot bushing/bearing are you using? Definitely in the clutch set up/system. What year T5 ? And what was it out of? Look up “ ultimate T5 thread” here on the Hamb tons of info on T5’s