completion functions not loaded

[Pier Paolo Grassi <pierpaolog@xxxxxxxxx>]

Hello, there are some completion functions that aren't loaded, it appears.

> functions _systemctl
_systemctl () {
        # undefined
        builtin autoload -XUz
}

systemctl<tab>

the output is from _files

systemctl<ctrl-h>

tags in context :completion::complete:SYSTEMD_PAGER=::
    argument-rest  (_arguments _gnu_generic)
tags in context :completion::complete:SYSTEMD_PAGER=:argument-rest:
    use-compctl    (_default _arguments _gnu_generic)
    globbed-files  (_files _default _arguments _gnu_generic)
tags in context :completion::complete:sudo::
    argument-rest  (_arguments _sudo)

it's not even listed. The completion function is defined in

/usr/share/zsh/vendor-completions

the dir is present in $fpath and other completion function from the same directory are working correctly.

What can I do to debug the issue?

thanks

Pier Paolo Grassi