Where should I start with the elytra, first up, if you use a firework, then land before it stops, then it doesn't stop, if you take off again before it stops, then you'll go flying up into the air, (easier to do with higher flight duration). Another glitch is of coarse the disappearing glitch, which I can't explain, but I have a picture lower down, it seems to happen if you go really fast, (e.g. when you use a firework). Another glitch I found is that fireworks make clouds behind them disappear, (also lower down). So I'm sorry, but you have a few things to fix with the elytra.