So I'm mining in my strip mine (a long land that is two blocks high and one wide) and I get cornered by a zombie. I hit him with my speed but I die due to low health. I come back to the mine in 1 minute and all of my stuff is gone. My enchanted diamond axe, my newly acquired diamonds, 52 glass panes, etc. I'm digging around and all I'm finding is stone, granite, and gravel, no lava.