From the documentation for the import/order rule's "groups" option:

The default value is ["builtin", "external", "internal", "parent", "sibling", "index"]

However, the rule's source file contains instead

const defaultGroups = ['builtin', 'external', 'parent', 'sibling', 'index']

where internal is missing. Not sure which of the two should be changed (I assume the source file), but this sent me on a wild goose chase this afternoon.