The /setblock command will only set the block IF where it is going to place it, is the chuck loaded. For example, I'm at x:0 y:50 z:0, and I use "/setblock 0 50 100 minecraft:snow 0 replace", this should set a block (snow block) at x:0 y:50 z:100, but this actually won't happen, this is because the chuck where the coordinates "x:0 y:50 z:100" are, isn't loaded.

If you want to fix this, you could use a "Chuck Loader" (for example, put the hoppers, one next to each other, and with an item inside one; just like a clock).