0. ALWAYS PROVIDE INFORMATION ABOUT MODLOADER (Fabric / Forge) AND MOD VERSION (For Example 1.19.2-8.2.10)

game version：1.20.1
forge 47.3.22
mod version：9.1.19

1. Describe the bug

After the server user hides the icon through the shortcut key, the backpack cannot be opened, and the original backpack items are also swallowed。

2. Write steps to reproduce the bug

Use shortcut keys to hide the icon and it will appear

3. What is expected behaviour
   fix the problem

4. Screenshots (If applicable)
   
   This is the error log generated by the server when opening the backpack。

What was in the backpack?

All items from the mod SlashBlade 2.
There are other players in the server who have the same items in their backpacks, but only the player with the backpack icon hidden has this error.

Do you mean this icon? I can hide it and still use it and I'm not sure if thats what you mean

Yes, the players on my server hid the icon of this place through the shortcut key.
By the way, my server core is mohist.

I can't reproduce this issue? Any player including you cant open backpack if hides the icon?

It's so strange. I tried it myself and couldn't reproduce the problem, but my friend did have this problem, and even the items in the original inventory disappeared.

My friend has Proud Soul from SlashBlade 2 in his backpack.

It's so strange. I tried it myself and couldn't reproduce the problem, but my friend did have this problem, and even the items in the original inventory disappeared.

if you cant reproduce this issue I think there's different cause of this. I cant reproduce it either

My friend just told me that he had this problem when he was spawning monsters in the Enderman Tower, and suddenly he couldn't open his backpack. But I tried it and still couldn't reproduce this problem, and every time I When a friend opens the backpack, the server's background will output the following log.

[20:18:12] [Server thread/ERROR] [net.minecraft.network.protocol.PacketUtils]: Failed to handle packet net.minecraft.network.protocol.game.ServerboundCustomPayloadPacket@47158968, suppressing error
java.lang.IllegalArgumentException: The PacketBuffer found for opening the GUI is invalid and is 53180 bytes long.
at net.minecraftforge.network.NetworkHooks.openScreen(NetworkHooks.java:208) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at com.tiviacz.travelersbackpack.inventory.BackpackContainer.openBackpack(BackpackContainer.java:61) ~[travelersbackpack-forge-1.20.1-9.1.19.jar%23456!/:forge-1.20.1-9.1.19]
at com.tiviacz.travelersbackpack.network.ServerboundSpecialActionPacket.lambda$handle$0(ServerboundSpecialActionPacket.java:51) ~[travelersbackpack-forge-1.20.1-9.1.19.jar%23456!/:forge-1.20.1-9.1.19]
at net.minecraftforge.network.NetworkEvent$Context.enqueueWork(NetworkEvent.java:212) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at com.tiviacz.travelersbackpack.network.ServerboundSpecialActionPacket.handle(ServerboundSpecialActionPacket.java:40) ~[travelersbackpack-forge-1.20.1-9.1.19.jar%23456!/:forge-1.20.1-9.1.19]
at net.minecraftforge.network.simple.SimpleChannel$MessageBuilder.lambda$consumerMainThread$1(SimpleChannel.java:272) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.NetworkEvent$Context.enqueueWork(NetworkEvent.java:212) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.simple.SimpleChannel$MessageBuilder.lambda$consumerMainThread$2(SimpleChannel.java:272) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.simple.IndexedMessageCodec.lambda$tryDecode$3(IndexedMessageCodec.java:115) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at java.util.Optional.ifPresent(Optional.java:178) ~[?:?]
at net.minecraftforge.network.simple.IndexedMessageCodec.tryDecode(IndexedMessageCodec.java:115) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:153) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:63) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:263) ~[eventbus-6.0.5.jar%23150!/:?]
at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:255) ~[eventbus-6.0.5.jar%23150!/:?]
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:319) ~[eventbus-6.0.5.jar%23150!/:?]
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:299) ~[eventbus-6.0.5.jar%23150!/:?]
at net.minecraftforge.network.NetworkInstance.dispatch(NetworkInstance.java:68) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraftforge.network.NetworkHooks.lambda$onCustomPayload$1(NetworkHooks.java:85) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at java.util.Optional.map(Optional.java:260) ~[?:?]
at net.minecraftforge.network.NetworkHooks.onCustomPayload(NetworkHooks.java:85) ~[forge-1.20.1-47.3.22-universal.jar%23467!/:?]
at net.minecraft.server.network.ServerGamePacketListenerImpl.m_7423_(ServerGamePacketListenerImpl.java:2892) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.network.protocol.game.ServerboundCustomPayloadPacket.m_5797_(ServerboundCustomPayloadPacket.java:37) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.network.protocol.game.ServerboundCustomPayloadPacket.m_5797_(ServerboundCustomPayloadPacket.java:10) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.network.protocol.PacketUtils.m_263899_(PacketUtils.java:25) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.TickTask.run(TickTask.java:18) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.util.thread.BlockableEventLoop.m_6367_(BlockableEventLoop.java:151) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.util.thread.ReentrantBlockableEventLoop.m_6367_(ReentrantBlockableEventLoop.java:23) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_6367_(MinecraftServer.java:1026) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_6367_(MinecraftServer.java:176) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.util.thread.BlockableEventLoop.m_7245_(BlockableEventLoop.java:124) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_129961_(MinecraftServer.java:1009) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_7245_(MinecraftServer.java:1003) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.util.thread.BlockableEventLoop.m_18701_(BlockableEventLoop.java:134) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_130012_(MinecraftServer.java:989) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_130011_(MinecraftServer.java:914) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at net.minecraft.server.MinecraftServer.m_206580_(MinecraftServer.java:286) ~[server-1.20.1-20230612.114412-srg.jar%23462!/:?]
at java.lang.Thread.run(Thread.java:840) [?:?]

Fix will be released today in about 5-6 hours

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack
Should be fixed