Unverified reproduction steps provided by Swekob:

1. Make sure you're not gliding with an elytra (stand on the ground or fly in creative mode).
2. Teleport to a high place with unloaded chunks where there is enough space to the ground to glide.
3. Try to glide with the elytra and observe the issue.

For example, you are on the coordinates of X:0 Y:10 Z:0. You're wearing an elytra. Then enter the command "/tp <your player name> 1000 100 1000" (if chunks in that area isn't loaded and if the Y coordinates is high enough to glide). You'll fall like a spike when you try to glide, like you normally would do without an elytra.

After an amount of teleportations the Elytra just stopped working.
After reloading the level it worked again. taking it out of the chest slot didn't solve the problem before.

https://www.youtube.com/watch?v=8EnHeXBgzqE&feature=youtu.be
Edit: New video showing how to recreate: https://www.youtube.com/watch?v=0xPxuxWQl6A&feature=youtu.be (to get the bug 100%, set the render distance to 2)