Put the summary of the bug you're having here

What I expected to happen was...:
When jumping from elevated level or using rockets, elytra should function

What actually happened was...:
Fell to death

Steps to Reproduce:
1. Built a tower
2. Jumped off
3. Activated elytra in normal manner
4. Fell to death

Within the same game session, the Elytra would inexplicably start working again, and then a minute or two later, stop.