one day I started minecraft (1.9) as usual and sudenly these walls appeared before me
I reinstalled minecraft 1.9 (deleted the 1.9 folder) but the problem was still there

What I expected to happen was...:
my World would load normaly so I could play

What actually happened was...:
my world loaded normaly and then strange walls appeared

Steps to Reproduce:
1. Open minecraft 1.9
2. Open a world OR join a server
3. note that strange walls are appearing