Minecraft 18w15a, Minecraft 18w19b, Minecraft 1.13-pre7, Minecraft 1.13-pre10, Minecraft 1.13, Minecraft 18w31a, Minecraft 18w32a, Minecraft 1.14.2, Minecraft 1.14.3, Minecraft 1.14.4 Pre-Release 2, 1.16.5
You input a command with an unknown name, or a missing but unrequired command, then the error message is not useful for it.
You input: /unknown
Error message: Unknown command at position 0: <--[HERE]
Expected: Unknown command "unknown". Type /help for help.
You input: /kill
Error message: Unknown command at position 4: /kill <--[HERE]
Expected: Missing variable: /kill <target> or "<target>" is a required variable.
Affected versions include earlier 1.13 snapshots, maybe since when the command system is changed.