((in another class)private ConcurrentHashMap<UUID, List<Location>> tileEntityLocations = new ConcurrentHashMap<>();
    private ConcurrentHashMap<Location, Material> tileEntityMaterials = new ConcurrentHashMap<>();)

public void checkChestVisibility() {
        for (Player player : Bukkit.getOnlinePlayers()) {
            if (previousplayerpos.containsKey(player.getUniqueId())) {
                if (!samelocation(previousplayerpos.get(player.getUniqueId()), player.getLocation())) {
                    List<Location> tileEntityLocations = Overseer.getESPLoader().getPacketChestHider1_13().getTileEntityLocations(player.getUniqueId());
                    if (tileEntityLocations != null) {
                        List<Location> remove = new ArrayList<>();
                       for (Location tLocation : tileEntityLocations) {
                            Location loc = player.getLocation();
                            World world = loc.getWorld();

                            if (world != tLocation.getWorld()) {
                                remove.add(tLocation);
                                continue;
                            }
                            int distanceSquared = (int) player.getLocation().distanceSquared(tLocation);

                            if (distanceSquared > 250 * 250) {
                                remove.add(tLocation);
                                continue;
                            }

                            if (distanceSquared < (8 * 8)) {
                                changeBlock(player, tLocation);
                                remove.add(tLocation);
                                continue;
                            }

                            if (distanceSquared < 2500) {

                                Vector3D actualEye = MathUtils.toUnitVector(
                                        Vector3D.fromLocation(player.getLocation().add(0, player.getEyeHeight(), 0)), 0.2,
                                        player.getLocation().getYaw(), player.getLocation().getPitch());

                                boolean shouldSeeChest = Utils.roughcheckChest(actualEye, tLocation, ischest(tLocation));

                                if (shouldSeeChest) {
                                    changeBlock(player, tLocation);
                                    remove.add(tLocation);
                                }
                            }
                        }
                        if (!remove.isEmpty()) {
                            ConcurrentHashMap<Location, Material> tileentitymaterials = Overseer.getESPLoader().getPacketChestHider1_13().getTileEntityMaterials();
                            for (Location l : remove) {
                                tileEntityLocations.remove(l);
                                tileentitymaterials.remove(l);
                            }
                            Overseer.getESPLoader().getPacketChestHider1_13().setTileEntityLocations(player.getUniqueId(), tileEntityLocations);
                            Overseer.getESPLoader().getPacketChestHider1_13().setTileEntityMaterials(tileentitymaterials);
                        }
                    }
                }
            }
            previousplayerpos.put(player.getUniqueId(), player.getLocation());
        }
    }


29.03 08:55:44 [Server] WARN [Overseer] Plugin Overseer v1.0 generated an exception while executing task 41445
29.03 08:55:44 [Server] INFO java.util.ConcurrentModificationException: null
29.03 08:55:44 [Server] INFO at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909) ~[?:1.8.0_212]
29.03 08:55:44 [Server] INFO at java.util.ArrayList$Itr.next(ArrayList.java:859) ~[?:1.8.0_212]
29.03 08:55:44 [Server] INFO at me.olly.overseer.AntiESP.v1_13.ChestHider.ChestHider1_13.checkChestVisibility(ChestHider1_13.java:30) ~[?:?]
29.03 08:55:44 [Server] INFO at me.olly.overseer.AntiESP.v1_13.Loader_v1_13.lambda$onEnable$0(Loader_v1_13.java:42) ~[?:?]
29.03 08:55:44 [Server] INFO at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftTask.run(CraftTask.java:84) ~[patched_1.15.2.jar:git-Paper-121]
29.03 08:55:44 [Server] INFO at org.bukkit.craftbukkit.v1_15_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:54) ~[patched_1.15.2.jar:git-Paper-121]
29.03 08:55:44 [Server] INFO at com.destroystokyo.paper.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:22) ~[patched_1.15.2.jar:git-Paper-121]
29.03 08:55:44 [Server] INFO at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [?:1.8.0_212]
29.03 08:55:44 [Server] INFO at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [?:1.8.0_212]
29.03 08:55:44 [Server] INFO at java.lang.Thread.run(Thread.java:748) [?:1.8.0_212]