When filling an area with End Gateway blocks, even after the beacon goes away, there is a huge loss of FPS while in looking at them that doesn't exists when fill a comparable area with End portals

To Recreate:
In creative, fly a bit above the ground
run this command
/fill ~-3 ~-2 ~-3 ~3 ~4 ~3 minecraft:end_gateway 0 outline
Watch the FPS plummet