I lost contact with discord. The server was in service. And now an error appears when loading DiscordCore and RustCord (respectively).
"Oxide.Ext.Discord is referenced by DiscordCore plugin but is not loaded! An appropriate include file needs to be saved to plugins\include\Ext.Discord.cs if this extension is not required."

Files versions:
"Discord", "seanbyrne88", "0.2.1"
"Discord Core", "MJSU", "2.0.3"
"DiscordMessages", "Slut", "2.1.8"
"Rustcord", "Kirollos & OuTSMoKE", "3.1.1"
"Oxide.Ext.Discord.dll" 2.0.2

Also, an error appeared on messages in the chat "Failed to call hook 'OnPlayerChat' on plugin 'BetterChat v5.2.7'"

I solved this problem myself. For some reason the "discord.config.json" file only contained "nul nul nul nul nul nul nul nul ...". I copied the config and rebooted the server - everything worked again.

You have both the Discord plugin and the Discord extension installed with the same name, you can't have both.