Do you have the crash report? (Located in .minecraft\crash-reports\crash-timestamp-client.txt)
It works for me in both creative and survival. Are you sure you were in the "flying" mode of the elytra when you tried to use the bost
Can you not join on any worlds?
That log message means that the tps was low for some reason (usually lag)
Confirmed for 1.11.2
This bug still works in 1.11 servers. The worst part is that you can use /tellraw Username [] to kick someone. This is annoying because people use it in realms and /kick does not work there. Please fix it in 1.11.1
That is BUD. Its bug but when you understand redstone its super useful. You can check https://www.youtube.com/watch?v=r5Wfzfq9kKs
If a crash happens on a modded server, there is no proof that it was vanilla's fault. This bug tracker is for vanilla only. If the crash does not happen in a vanilla server, then contact staff team of cubecraft