/give @a does not work in a command block.

After a player has died, a /give command from a command block will spawn items at their spawnpoint instead of to the player.

Re-entering the world fixes the issue until you die.

The screenshot shows the stone appearing at point that is not me.

This is a duplicate issue of MC-44521. MC-44521 does a better job of explaining the bug, refer to it for more info.