I'm getting a weird bug on my server. It seems to come up sporadically, and only on certain players. One of my players, while testing today, found that he was invulnerable to damage from mobs. They would still crowd around him and shoot at him, but he would take no damage from them (nor was there the animation indicating that something had been damaged). He also took no damage when I shot at him. However, after a couple minutes, the mobs started hitting him and he died, but then he became invulnerable again shortly after. Even while invulnerable to mobs, though, he could still kill himself by drowning. I checked for godmode and creative mode, and neither of those were on for him. I also checked to make sure he wasn't in any worldguard region that might have been giving him the invulnerability. It is unlikely that he was using a hacked client, as I have NoCheatPlus installed and I was able to verify that he was using Spoutcraft (hacked spoutcraft clients are hard to come by, from what I understand). I checked the server logs and there were no errors, and his permission nodes didn't indicate anything abnormal (and he's not an OP or anything). I have an extremely long list of plugins, but none of them seem relevant to the issue. They are as follows: Spoiler (Move your mouse to the spoiler area to reveal the content) Show Spoiler Hide Spoiler afkTerminator AnkleBrace Assassin Attila backpack-b148 BKCommonLib-1.56 BookShelf BookSuite boosCooldowns BorderVisualizer bPermissions Brewery-1.1 Cannons ChestShop cncp (Compat NoCheatPlus) Coinage-0.2.2 CombatTag Courier CrackShot CraftBook CreatYourOwnMenus CreeperHeal DeathAndRebirth DispNameChanger DrugMeUp dsTitle Essentials EssentialsAntiBuild ExtraHardMode HeroChat InteractBlock LandSlide LoreLocks MagicSpells MagicSpellsCastModifier Meow MinecartMania MineralManager MonsterApocalypse Morehearts MoreMaterials-2.1 Movecraft Multiverse-Core-2.5 Multiverse-Inventories-2.5 Multiverse-NetherPortals-2.5 Multiverse-Portals-2.5 Multiverse-SignPortal-2.5 NeverBreak NoCheatPlus NoItem NoVillagerTrading PwnPlantGrowth Questioner QuickTrade RealisticExplosives signcodepad-2.2.0 SignEditor Soulbound SparkTrail spoutcraftplugin-1.6.4-b1 SuperPotions thejoyofpainting TimeFold Towny TownyMobs TPC TrainCarts-1.72.9 VanishNoPacket VariableTriggers Vault WorldBorder worldedit-5.5.8 worldguard-5.5.8 Does anyone know what might be causing this? EDIT: Oh, yes, and I'm on Spigot 1.6.4-R2.1, although that's probably not relevant since this problem has cropped up on and off for longer than we've had this build.