Read Desc.

Does someone know why this function spawns Chests only at y = 128?

PHP:

public function generateChest(Level $level)
    {
        $x = mt_rand(-200, 200);
        $z = mt_rand(-200, 200);
       
        $catch = [1, 9];
       
        for($y=1; $y<=128; $y++)
        {
            if(in_array($level->getBlockIdAt($x, $y, $z), $catch, true))
            {           
                $block = new \pocketmine\block\Chest();
                $level->setBlock(new Vector3($x, $y-1, $z), $block, true, true);
                $nbt = new Compound("", [
                        new Enum("Items", []),
                        new String("id", Tile::CHEST),
                        new Int("x", $x),
                        new Int("y", $y),
                        new Int("z", $z)
                            ]);
                $nbt->Items->setTagType(NBT::TAG_Compound);
                $tile = Tile::createTile("Chest", $level->getChunk($block->getX() >> 4, $block->getZ() >> 4), $nbt);
                $tile->getInventory()->clearAll();
                for($i=0;$i<=26;$i++)
                {
                    $rand = mt_rand(1, 5);
                    if($rand === 1)
                    {
                        $items = array
                        (
                            Item::get(298, 0, 1),
                            Item::get(299, 0, 1),
                            Item::get(300, 0, 1),
                            Item::get(301, 0, 1),
                            Item::get(268, 0, 1),
                            Item::get(271, 0, 1),

                            Item::get(297, 0, 1),

                            Item::get(393, 0, 1),
                            Item::get(393, 0, 3),

                            Item::get(265, 0, 1),
                            Item::get(265, 0, 3),
                            Item::get(265, 0, 8),

                            Item::get(266, 0, 1),
                            Item::get(266, 0, 3),

                            Item::get(264, 0, 1),
                            Item::get(264, 0, 2),

                            Item::get(272, 0, 1),

                            Item::get(320, 0, 1),
                            Item::get(320, 0, 3),

                            Item::get(364, 0, 1),
                            Item::get(364, 0, 3),

                            Item::get(366, 0, 1),
                            Item::get(366, 0, 3),

                            Item::get(Item::COMPASS, 0, 1),
                            Item::get(Item::COMPASS, 0, 1)
                        );
                            $itemRnd = mt_rand(0, count($items)-1);
                            $item = $items[$itemRnd];

                            $tile->getInventory()->setItem($i, $item);
                        } else {
                            $tile->getInventory()->setItem($i, Item::get(0, 0, 1));
                        }
                    }
                }
            }    
           
            $this->getServer()->broadcastMessage($x . " " . $y . " " . $z);
    }

Maybe condition is false? Anyway try to debug your code it should help you

ok ^^