corruption in my world infront of my eyes

i played on my minecraft world i have this world 5 years and today something strange happend some of my old chunks replaced in a trail of new .on my builds 

idk how it happend. but i know its not something that supposed to happend. 

i send screenshots in case you don't believe me.

for the protocol i played this world yesterday before i got to sleep and it was okay in the morning(today) not