Dedicated server crash

Appears only to occur when I connect to the server. others can connect without issue. takes between 10 and 20 seconds to crash.

world was created in 20w21a yesterday.

---- Minecraft Crash Report ----
// But it works on my machine.
Time: 24/05/20 12:52
Description: Watching Server
java.lang.Error
 at xz.run(SourceFile:48)
 at java.lang.Thread.run(Thread.java:748)

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------
-- Head --
Thread: Server Watchdog
Stacktrace:
 at xz.run(SourceFile:48)
-- Thread Dump --
Details:
 Threads: "Worker-Main-11" Id=36 WAITING on java.util.concurrent.CompletableFuture$Signaller@13bcb8b1
 at sun.misc.Unsafe.park(Native Method)
 - waiting on java.util.concurrent.CompletableFuture$Signaller@13bcb8b1
 at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
 at java.util.concurrent.CompletableFuture$Signaller.block(CompletableFuture.java:1707)
 at java.util.concurrent.ForkJoinPool.managedBlock(ForkJoinPool.java:3313)
 at java.util.concurrent.CompletableFuture.waitingGet(CompletableFuture.java:1742)
 at java.util.concurrent.CompletableFuture.join(CompletableFuture.java:1947)
 at yu.a(SourceFile:124)
 at bpa.a(SourceFile:242)
 ...

"Netty Epoll Server IO #1" Id=32 RUNNABLE
 at io.netty.channel.epoll.Native.epollWait0(Native Method)
 at io.netty.channel.epoll.Native.epollWait(Native.java:114)
 at io.netty.channel.epoll.EpollEventLoop.epollWait(EpollEventLoop.java:239)
 at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:256)
 at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
 at java.lang.Thread.run(Thread.java:748)

"Server Watchdog" Id=31 RUNNABLE
 at sun.management.ThreadImpl.dumpThreads0(Native Method)
 at sun.management.ThreadImpl.dumpAllThreads(ThreadImpl.java:454)
 at xz.run(SourceFile:45)
 at java.lang.Thread.run(Thread.java:748)

"IO-Worker-10" Id=29 TIMED_WAITING on java.util.concurrent.SynchronousQueue$TransferStack@1d7b44b6
 at sun.misc.Unsafe.park(Native Method)
 - waiting on java.util.concurrent.SynchronousQueue$TransferStack@1d7b44b6
 at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
 at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
 at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
 at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 ...

"IO-Worker-8" Id=27 TIMED_WAITING on java.util.concurrent.SynchronousQueue$TransferStack@1d7b44b6
 at sun.misc.Unsafe.park(Native Method)
 - waiting on java.util.concurrent.SynchronousQueue$TransferStack@1d7b44b6
 at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:215)
 at java.util.concurrent.SynchronousQueue$TransferStack.awaitFulfill(SynchronousQueue.java:460)
 at java.util.concurrent.SynchronousQueue$TransferStack.transfer(SynchronousQueue.java:362)
 at java.util.concurrent.SynchronousQueue.poll(SynchronousQueue.java:941)
 at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1073)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 ...

"Netty Epoll Server IO #0" Id=22 RUNNABLE
 at io.netty.channel.epoll.Native.epollWait0(Native Method)
 at io.netty.channel.epoll.Native.epollWait(Native.java:114)
 at io.netty.channel.epoll.EpollEventLoop.epollWait(EpollEventLoop.java:239)
 at io.netty.channel.epoll.EpollEventLoop.run(EpollEventLoop.java:256)
 at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:884)
 at java.lang.Thread.run(Thread.java:748)

"ObjectCleanerThread" Id=21 TIMED_WAITING on java.lang.ref.ReferenceQueue$Lock@1944d3c1
 at java.lang.Object.wait(Native Method)
 - waiting on java.lang.ref.ReferenceQueue$Lock@1944d3c1
 at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
 at io.netty.util.internal.ObjectCleaner$1.run(ObjectCleaner.java:54)
 at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
 at java.lang.Thread.run(Thread.java:748)

"DestroyJavaVM" Id=19 RUNNABLE

"Server Infinisleeper" Id=17 TIMED_WAITING
 at java.lang.Thread.sleep(Native Method)
 at xw$1.run(SourceFile:88)

"Snooper Timer" Id=15 WAITING on java.util.TaskQueue@5c464e8d
 at java.lang.Object.wait(Native Method)
 - waiting on java.util.TaskQueue@5c464e8d
 at java.lang.Object.wait(Object.java:502)
 at java.util.TimerThread.mainLoop(Timer.java:526)
 at java.util.TimerThread.run(Timer.java:505)

"Signal Dispatcher" Id=4 RUNNABLE

"Finalizer" Id=3 WAITING on java.lang.ref.ReferenceQueue$Lock@2ac91c84
 at java.lang.Object.wait(Native Method)
 - waiting on java.lang.ref.ReferenceQueue$Lock@2ac91c84
 at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:144)
 at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:165)
 at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:216)

"Reference Handler" Id=2 WAITING on java.lang.ref.Reference$Lock@6dd0b39f
 at java.lang.Object.wait(Native Method)
 - waiting on java.lang.ref.Reference$Lock@6dd0b39f
 at java.lang.Object.wait(Object.java:502)
 at java.lang.ref.Reference.tryHandlePending(Reference.java:191)
 at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:153)
 
Stacktrace:
 at xz.run(SourceFile:48)
 at java.lang.Thread.run(Thread.java:748)
-- System Details --
Details:
 Minecraft Version: 20w21a
 Minecraft Version ID: 20w21a
 Operating System: Linux (amd64) version 4.9.0-11-amd64
 Java Version: 1.8.0_242, Oracle Corporation
 Java VM Version: OpenJDK 64-Bit Server VM (mixed mode), Oracle Corporation
 Memory: 9559184640 bytes (9116 MB) / 12697731072 bytes (12109 MB) up to 12697731072 bytes (12109 MB)
 CPUs: 4
 JVM Flags: 2 total; -Xmx12G -Xms12G
 Player Count: 1 / 20; [yx['Tirpitz93'/96, l='ServerLevel[world]', x=-146.28, y=72.00, z=396.70]]
 Data Packs: vanilla
 Is Modded: Unknown (can't tell)
 Type: Dedicated Server (map_server.txt)root@minecraft:/home/loenja#

```