Disappearing blocks

Hi,
Something very strange happened on my server.
Before I had left the server, some blocks didn't load. It looked like those "chunks aren't loading" issues (black areas on builds). I ran the commands /save-all and then /stop.
After I had joined again, the blocks, where the big black area was, were gone. A big part was missing on my statue.

(You can see that the missing part has a shape like a cuboid)