I am encountering this "invalid player data" as well on Minecraft Java client 1.20.2 when connecting to the latest Paper 1.20.2 Build 249.
I created a new VM (2core 8gb RAM), installed and ran Vanilla Minecraft 1.20.2, and tested I could connect via my Minecraft client successfully. Then...
1) I stopped the Minecraft "server.java" process.
2) Replaced the (vanilla) server.jar with "paper-1.20.2-249.jar"
3) Started Paper - logs show it migrated world data, etc.
However, when I try to connect my Minecraft client, I receive "Invalid Player Data" and the paper server log shows:
[21:34:00] [User Authenticator #0/INFO]: UUID of player damenthb is <REMOVED_MY_GUID>
[21:34:00] [Server thread/ERROR]: Couldn't place player in world
java.lang.NullPointerException: Cannot invoke "net.minecraft.server.level.WorldServer.ac()" because the return value of "net.minecraft.server.level.EntityPlayer.x()" is null
at net.minecraft.server.players.PlayerList.placeNewPlayer(PlayerList.java:224) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.server.network.ServerConfigurationPacketListenerImpl.handleConfigurationFinished(ServerConfigurationPacketListenerImpl.java:130) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.network.protocol.configuration.ServerboundFinishConfigurationPacket.handle(ServerboundFinishConfigurationPacket.java:18) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.network.protocol.configuration.ServerboundFinishConfigurationPacket.a(ServerboundFinishConfigurationPacket.java:9) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.network.protocol.PacketUtils.lambda$ensureRunningOnSameThread$0(PacketUtils.java:53) ~[?:?]
at net.minecraft.server.TickTask.run(TickTask.java:18) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:153) ~[?:?]
at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[?:?]
at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1324) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:193) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:126) ~[?:?]
at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1301) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1294) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:136) ~[?:?]
at net.minecraft.server.MinecraftServer.waitUntilNextTick(MinecraftServer.java:1272) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1160) ~[paper-1.20.2.jar:git-Paper-249]
at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:315) ~[paper-1.20.2.jar:git-Paper-249]
at java.lang.Thread.run(Thread.java:833) ~[?:?]
[21:34:00] [Server thread/INFO]: com.mojang.authlib.GameProfile@3e95d21d[id=2aaee500-f9fa-45f5-9bdc-20eafd15a204,name=damenthb,properties={textures=[Property[name=textures, value=ewogICJ0aW1lc3RhbXAiIDogMTY5ODQ0MjQ0MDQ5NywKICAicHJvZmlsZUlkIiA6ICIyYWFlZTUwMGY5ZmE0NWY1OWJkYzIwZWFmZDE1YTIwNCIsCiAgInByb2ZpbGVOYW1lIiA6ICJkYW1lbnRoYiIsCiAgInNpZ25hdHVyZVJlcXVpcmVkIiA6IHRydWUsCiAgInRleHR1cmVzIiA6IHsKICAgICJTS0lOIiA6IHsKICAgICAgInVybCIgOiAiaHR0cDovL3RleHR1cmVzLm1pbmVjcmFmdC5uZXQvdGV4dHVyZS9mNWRkZGI0MWRjYWZlZjYxNmU5NTljMjgxNzgwOGUwYmU3NDFjODlmZmJmZWQzOTEzNGExM2U3NWI4MTE4NjNkIgogICAgfQogIH0KfQ==, signature=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]]}] lost connection: Invalid player data
Any thoughts?
Thank you!