Architectury & REI Server Packet Error: Cannot invoke class_8710$class_9154.comp_2242() because "type" is null

What the log looks like

java\.lang\.NullPointerException: Cannot invoke "net\.minecraft\.class_8710\$class_9154\.comp_2242\(\)" because "type" is null
dev\.architectury\.impl\.NetworkAggregator\.collectPackets\(NetworkAggregator\.java:\d+\)

How to fix it

1. Update Roughly Enough Items (REI), Architectury API, and Fabric API to the latest available versions on both the dedicated server and all players' clients.
2. Check whether the server actually stopped running; this log entry is usually a non-fatal task exception on the server thread, meaning gameplay continues normally aside from REI's tag tree window failing to load.
3. Run `/reload` on the server or ask players to avoid opening REI's tag viewer (`$` search or tag tree menu) as a temporary workaround if no newer REI build is available for your Minecraft version yet.
4. If you do not rely on REI's server-side recipe transfer or cheat mode features, remove the `RoughlyEnoughItems` jar from the dedicated server's `mods` folder while leaving it installed on clients.

Check your own log