To repro this multiple players are needed to be exploring the world- 10 or more appears to do it.

---- Minecraft Crash Report -------- Minecraft Crash Report ----// Don't be sad. I'll do better next time, I promise!
Time: 5/1/19 7:03 PMDescription: Exception ticking world
java.util.ConcurrentModificationException at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909) at java.util.ArrayList$Itr.next(ArrayList.java:859) at net.minecraft.server.v1_14_R1.TickListServer.a(TickListServer.java:72) at net.minecraft.server.v1_14_R1.WorldServer.doTick(WorldServer.java:271) at net.minecraft.server.v1_14_R1.MinecraftServer.b(MinecraftServer.java:1054) at net.minecraft.server.v1_14_R1.DedicatedServer.b(DedicatedServer.java:396) at net.minecraft.server.v1_14_R1.MinecraftServer.a(MinecraftServer.java:953) at net.minecraft.server.v1_14_R1.MinecraftServer.run(MinecraftServer.java:798) at java.lang.Thread.run(Thread.java:748)