No, there are no add-ons applied to the world.
Edit: It's just a normal Hardcore Minecraft world.
Yes, I am currently on the newest version of Chrome-OS. I've even tried restarting Minecraft, with mixed results; Sometimes it worked, sometimes it didn't.
I forgot to mention, I even took off my texture pack, and it still was happening.
No, there are no add-ons applied to the world.
Edit: It's just a normal Hardcore Minecraft world.