The bug
Summoning in a bee with a passenger crashes the game, rendering the affected world inaccessible because it causes further crashes.
Crash report
19w34a\: [^crash-2019-08-23_07.16.02-server.txt]
Description: Ticking entity
java.lang.ClassCastException: asb$1 cannot be cast to aqo
at awk.L(SourceFile:100)
at ajy.dh(SourceFile:631)
at ajx.k(SourceFile:2288)
at ajy.k(SourceFile:487)
at avu.k(SourceFile:39)
at aym.k(SourceFile:114)
at ajx.h(SourceFile:2133)
at ajy.h(SourceFile:294)
at avu.h(SourceFile:51)
at ajo.aN(SourceFile:1648)
at ajx.aN(SourceFile:2427)
at wj.a(SourceFile:613)
at wj.a(SourceFile:591)
at wj$$Lambda$2769/586961333.accept(Unknown Source)
at bit.a(SourceFile:675)
at wj.a(SourceFile:386)
at net.minecraft.server.MinecraftServer.b(SourceFile:836)
at net.minecraft.server.MinecraftServer.a(SourceFile:775)
at ebt.a(SourceFile:128)
at net.minecraft.server.MinecraftServer.run(SourceFile:643)
at java.lang.Thread.run(Thread.java:745)
Thank you for your report!
We're actually already tracking this issue in MC-158484, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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