work I did despawned

I was about to build a house on an island, then I started building a dock. I placed some blocks but then stopped and went to gather more materials. I came back and finished the dock. Then I went to gather materials for the house. I dug up some sand then went to harvest some wood. When I came back all of the sand that I had harvested was back in its original position but I still had all the sand I got from it in my inventory, and the dock was like it was before I came back to finish it, yet the materials i had used to finish the dock were no longer in my inventory. This happened without me logging off at any time (until after it happened because I rage quit).