Elytra not working!

Put the summary of the bug you're having here

What I expected to happen was the elytra to work after I'd use the end gateways and pree my jump key, but it didn't work.
I thought the elytra would activate after pressing my jump key instead of falling to my death.

What actually happened was when I jumped off a tower that I made to fly to other end cities and as I pressed my jump key it didn't work, luck I had keepinventory on.

Steps to Reproduce:
1. Enter the end
2.Build up very high
3. jump and press your jump key