Sticky piston slime block glitch

I tried to build the blaze farm outlined by nims tv on youtube.

tutorial can be found here. https://www.youtube.com/watch?v=XORCrgVinIo

what i've notice is that my slime blocks are teleporting instead of sliding across the furnaces that I've placed as the "floor" of the cage.

I tried to test and see if the farm worked by standing in the path of the slime blocks to see if i would be pushed into the collection area, and my avatar is only pushed a little bit back and forth. So the slime blocks are not updating enough to push mobs off the platform the way that they should.