Maybe not the same, but I'm having the same problem. Hosted locally with "Open to Lan".
Code:
[06Feb2021 13:25:04.070] [Render thread/INFO] [Astral Sorcery/]: Client cache cleared!
[06Feb2021 13:25:04.077] [Render thread/INFO] [net.minecraft.client.gui.screen.ConnectingScreen/]: Connecting to 192.168.2.107, 51569
[06Feb2021 13:25:04.624] [Render thread/INFO] [Astral Sorcery/]: Built PerkTree with 417 perks!
[06Feb2021 13:25:07.611] [Render thread/ERROR] [net.minecraftforge.fml.network.FMLHandshakeHandler/FMLHANDSHAKE]: Missing registry data for network connection:
minecraft:block: industrialforegoing:milk_block
[06Feb2021 13:25:07.611] [Netty Client IO #5/ERROR] [net.minecraftforge.fml.network.FMLHandshakeHandler/FMLHANDSHAKE]: Failed to load registry, closing connection.
[06Feb2021 13:25:07.611] [Netty Client IO #5/ERROR] [net.minecraftforge.fml.network.FMLHandshakeHandler/FMLHANDSHAKE]: Connection closed, not continuing handshake
Not sure if there is anywhere I can get more specific networking logs. We are both on the same version, tried to reinstall the modpack on the client user but still same issue.
EDIT: Oh actually looks like that minecraft:block: industrialforegoing:milk_block could be the issue right? Any way to do a local fix without waiting for a modpack update?