Jeeez man. Slow the reel down or increase the forward speed. Theres 2 things happening there. The reel is shattering grain from being to low and fast and b, the feed cannot be even into the machine thus, lowering treshing capacity. If you cannot feed it without the rel that fast, bring your auger forward a tad.
I've cut heavy crops on Europe and that looked like a well ripened 3-4 ton crop what had some rain on it. That stuff should come off real fast.