[12:28:36] [Server thread/ERROR]: Couldn't save chunk; already in use by another instance of Minecraft?
aui: Failed to check session lock, aborting
        at bvx.c(SourceFile:86) ~[server.jar:?]
        at aug.O(SourceFile:2682) ~[server.jar:?]
        at bio.a(SourceFile:177) ~[server.jar:?]
        at sd.b(SourceFile:225) [server.jar:?]
        at sd.d(SourceFile:287) [server.jar:?]
        at se.k_(SourceFile:199) [server.jar:?]
        at net.minecraft.server.MinecraftServer.w(SourceFile:694) [server.jar:?]
        at rp.w(SourceFile:354) [server.jar:?]
        at net.minecraft.server.MinecraftServer.v(SourceFile:627) [server.jar:?]
        at net.minecraft.server.MinecraftServer.run(SourceFile:532) [server.jar:?]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_161]