After changing render distance (8 originally switched to 16) some areas are just visually repeating the same chunk and it just changes all the time. You can move threw it as there was nothing. Leaving the map and coming in again don't change anything but closing the game and relaunch it clears the bug.
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Sorry about the duplicate, i did try to check if it was already existing...
Still the real original one is this one :
https://bugs.mojang.com/browse/MC-62958
Over 50 people are as stupid as me creating duplicates ! \o/