CT Issue here

Thought you may want to take a peek. @chikachi

In the v3 alpha version, the message is different. Command is not executed still..
[JDA MainWS-ReadThred/WARN] [Sponge]: No entity type is registered for class chikachi.discord.command.DiscordCommandSender

This is expected behaviour from SpongeForge

While it's normally a sign that a mod is doing something wrong, the two classes mentioned above appear to be various 'fake player' classes. Since these never actually get spawned into the world, you can safely ignore them.
SpongePowered/SpongeForge#1272 (comment)