I get this error sometimes

[20:54:19] [pool-7-thread-10/WARN]: Unknown CommandBlock failed to handle command
java.lang.IllegalStateException: Asynchronous entity add!
at org.spigotmc.AsyncCatcher.catchOp(AsyncCatcher.java:14) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.World.addEntity(World.java:991) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.World.addEntity(World.java:987) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.EntityHuman.a(EntityHuman.java:630) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.EntityHuman.a(EntityHuman.java:620) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.EntityHuman.drop(EntityHuman.java:558) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at net.minecraft.server.v1_8_R3.CommandGive.execute(SourceFile:72) ~[spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at org.bukkit.craftbukkit.v1_8_R3.command.VanillaCommandWrapper.dispatchVanillaCommand(VanillaCommandWrapper.java:108) [spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at org.bukkit.craftbukkit.v1_8_R3.command.VanillaCommandWrapper.execute(VanillaCommandWrapper.java:43) [spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) [spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:641) [spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at org.bukkit.Bukkit.dispatchCommand(Bukkit.java:576) [spigot-1.8.8.jar:git-Spigot-76236cb-c373061]
at com.rogue.playtime.callable.ConsoleCommandCallable.call(ConsoleCommandCallable.java:37) [Playtime.jar:?]
at java.util.concurrent.FutureTask.run(Unknown Source) [?:1.8.0_60]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(Unknown Source) [?:1.8.0_60]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source) [?:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) [?:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) [?:1.8.0_60]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_60]

This is not a fault of Playtime, Playtime has nothing to do with entities.

well this error still only happens after com.rogue.playtime.callable.ConsoleCommandCallable.call it never happens otherwise

it happens when playtime execute a give command with the following events.yml

exampletwo:
type: onlinetime
time: 120
at-login: false
repeat: true
commands:
- 'msg %u Here''s some food for being online so much!'
- 'give %u cooked_beef 1'

Might be a fault when attempting to add an item to a player with a full inventory, causing an item drop.

é só usar sync