Sugarcane disappears when slime block hits it in some cases

I built a sugarcane farm as shown in the picture. It makes use of a flying machine to break the sugarcane and a hopper-minecart (underneath the farm) to collect. In the image, the bottom half of the farm works fine, the sugarcane shoots off the slime blocks when the flying machine makes contact with it. However, on the top half of the farm in the image, the sugarcane simply disappears when coming into contact with the slime, as shown in the video. When the flying machine is returning (going opposite to what is shown in the video) the problem is flipped as in the bottom half of the farm in the image is broken and the top half is fine. And yes, I checked the hopper, nothing in there.