It looks like a synchronization issue. Gridindex += value with the same index value may be executed concurrently by several work items. This operation is not atomic, and all these work items will load gridindex add their value, and store it back, possibly losing some increments in the process.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.