I have a strange behavior in AUCTeX with RefTeX: the command 'reftex-reference' (C-c )) needs to be run before the command 'reftex-cleveref-cref' gets recognized, on a newly-started emacs session.

In other words, the command 'reftex-cleveref-cref' looks non-existing if I did not run any 'reftex-reference' yet.

What would be the explanation?