I've been working on a minigame map. I generated the world Superflat on Survival with Cheats so I could go into Creative to build it.
My Redstone setup for this is as follows:
Player presses button
Redstone trail goes to a command block: /say Game starts in 5...
Trail continues to command block: /say 4...
Trail continues to command block: /say 3...
Trail continues to command block: /say 2...
Trail continues to command block: /say 1...
Trail continues to 3 command blocks that activate simultaneously.
Command Block A: /say Go!
Command Block B: /tp @a (coords)
Command Block C: /spawnpoint @a (coords)
A and B work fine, but C doesn't do anything. It's basically dead, it doesn't even say that it set the spawnpoint of all players. I tested to see if I just placed it in a bad spot and changed the command, and it worked with that. I put /spawnpoint back in and it didn't do anything still. Unfortunately, my map won't work until this issue is fixed.
Make sure that 1: your coordinates are whole numbers and not decimal, and 2: the chunk that has the command block is still loaded. Although they are set to activate "simultaneously", they do in fact load in a certain order, and if (between the tp and spawnpoint commands) the chunk is unloaded, it's possible the command won't execute.