I recently updated a 1.17.1 server (that was originally created on 1.16.3) to 21w39a. Aside from the expected extra lag and longer world generation time, the console gets filled with these errors:
[08:25:33] [Server thread/ERROR]: No key feature in MapLike[{blacklist:[],block_placer:
{type:"minecraft:simple_block_placer"}
,can_replace:0b,need_water:0b,project:1b,state_provider:{type:"minecraft:plain_flower_provider"},tries:64,whitelist:[],xspread:7,yspread:3,zspread:7}]; No key only_in_air in MapLike[{blacklist:[],block_placer:
{type:"minecraft:simple_block_placer"}
,can_replace:0b,need_water:0b,project:1b,state_provider:{type:"minecraft:plain_flower_provider"},tries:64,whitelist:[],xspread:7,yspread:3,zspread:7}]; No key disallowed_on in MapLike[{blacklist:[],block_placer:
{type:"minecraft:simple_block_placer"}
,can_replace:0b,need_water:0b,project:1b,state_provider:{type:"minecraft:plain_flower_provider"},tries:64,whitelist:[],xspread:7,yspread:3,zspread:7}]; No key allowed_on in MapLike[{blacklist:[],block_placer:
{type:"minecraft:simple_block_placer"}
,can_replace:0b,need_water:0b,project:1b,state_provider:{type:"minecraft:plain_flower_provider"},tries:64,whitelist:[],xspread:7,yspread:3,zspread:7}]
[08:25:33] [Server thread/ERROR]: Exception loading structure piece with id minecraft:jigsaw
java.lang.IllegalStateException: Invalid pool element found
at ddx.k(SourceFile:54) ~[server-21w39a.jar:?]
at java.util.Optional.orElseThrow(Optional.java:403) ~[?:?]
at ddx.<init>(SourceFile:54) ~[server-21w39a.jar:?]
at dem.a(SourceFile:74) ~[server-21w39a.jar:?]
at cwo.a(SourceFile:138) ~[server-21w39a.jar:?]
at cpq.a(SourceFile:429) ~[server-21w39a.jar:?]
at cpq.a(SourceFile:185) ~[server-21w39a.jar:?]
at abp.m(SourceFile:580) ~[server-21w39a.jar:?]
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1764) ~[?:?]
at asx.c(SourceFile:151) ~[server-21w39a.jar:?]
at aca$b.c(SourceFile:534) ~[server-21w39a.jar:?]
at asx.z(SourceFile:125) ~[server-21w39a.jar:?]
at aca$b.z(SourceFile:543) ~[server-21w39a.jar:?]
at aca.d(SourceFile:278) ~[server-21w39a.jar:?]
at net.minecraft.server.MinecraftServer.bf(SourceFile:770) ~[server-21w39a.jar:?]
at net.minecraft.server.MinecraftServer.z(SourceFile:758) ~[server-21w39a.jar:?]
at asx.bp(SourceFile:110) ~[server-21w39a.jar:?]
at net.minecraft.server.MinecraftServer.y(SourceFile:742) ~[server-21w39a.jar:?]
at net.minecraft.server.MinecraftServer.x(SourceFile:693) ~[server-21w39a.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:274) ~[server-21w39a.jar:?]
at java.lang.Thread.run(Thread.java:831) [?:?]
I only get these if I join the game around the oldest area on the server. I have also noticed that there doesn't seem to be a single item frame in the entire world, even though I swear I placed one before the switch. These errors do not crash the client or server.
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The log spam when upgrading 1.16.x chunks is MC-227945, but the missing item frames might be a different bug. I attempted to reproduce the disappearance of item frames that you said happened on your world. I created a world in 1.16.5, placed down some item frames, and upgraded it to 21w39a. The item frames were still there after opening the world in 21w39a. If you are sure that you actually placed an item frame in your world before upgrading it, please make a new report about that and include steps to reproduce the missing item frames.
Thank you for your report!
We're tracking this issue in MC-227945, so this ticket is being resolved and linked 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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