World being destroyed by the appearance of huge anormal blocks

On my main save, a survival adventure that I play and like a lot, strange chunks have appeared once when I launched the game. I thought it was funny at first but a bit strange, and it wasn't really a problem because it wasn't really affecting me. I play a little and leave the game. But later that day, as I wanted to play again and started the game, black screen, lifepoint loss and boom, I die and it says "XaeS_TheoS suffocated in a wall" or something like that : one of these huge blocks had appeared on my house, where I was when I saved and quit the game earlier that day. The only problem isn't that it killed me, because I can easily respawn : the problem is that it "swallowed" my house, replacing it by other blocks and destroying a lot of things I had built and killing almost all of the animals I had.

Why ? What happened ? Will it get worse ? Is my game broken ? Is that save file now unplayable ?

If that can help, I have screenshots of this issue.