[23:10:06] [Server thread/FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
        at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_211]
        at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_211]
        at net.minecraft.util.Util.func_181617_a(Util.java:51) [h.class:?]
        at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:846) [MinecraftServer.class:?]
        at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:473) [nz.class:?]
        at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:783) [MinecraftServer.class:?]
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:637) [MinecraftServer.class:?]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_211]
Caused by: java.lang.NullPointerException
        at com.pixelmonmod.pixelmon.comm.packetHandlers.ReplaceMove$Handler.onSyncMessage(ReplaceMove.java:132) ~[ReplaceMove$Handler.class:?]
        at com.pixelmonmod.pixelmon.comm.packetHandlers.ReplaceMove$Handler.onSyncMessage(ReplaceMove.java:88) ~[ReplaceMove$Handler.class:?]
        at com.pixelmonmod.pixelmon.api.comm.ISyncHandler.lambda$onMessage$0(ISyncHandler.java:17) ~[ISyncHandler.class:?]
        at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_211]
        at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_211]
        at net.minecraft.util.Util.func_181617_a(Util.java:50) ~[h.class:?]

请发送完整的错误报告

com.pixelmonmod.pixelmon.comm.packetHandlers.ReplaceMove$Handler.onSyncMessage(ReplaceMove.java:132) ~[ReplaceMove$Handler.class:?]
宝可梦mod同步消息时出了bug，重启大概率可解决，或者更新一个，如果有的话。

像楼上说的 宝可梦mod有问题

建议更换宝可梦mod版本

比如更新到最新版或者降级