It could a number of things, you don't say what generation or device type etc. so specific's will be lacking.  Some devices are made with extra blocks and during test if a block is found bad the other block is routed into it's place through programmable switches.

The routing channels for the substitutional blocks may have gone bad and depending upon the location of the blocks that could also explain why the pattern that you are seeing (2 blocks separated by one).

The most likely situation is that the chip died, or was hurt with ESD.  

Flash Memory Failure Modes - Block Failure
I think the title says it all. Let's say you're mastering a game without the benefit of miniatures, maps, or any kind of physical representation of the environment. How would you keep track of details like line-of-sight, ranged attack viability, and all the other small nuances which go with creating a "believable-enough" environment in which your PCs live and thrive?

(I admit that @LoganMacRae, who is my own DM, is an inspiration for this question. He does this with panache, and in my one-off, I feel like I have some mighty big shoes to fill!)
