Kuba Orlik via "Bug reports for GNU Emacs, the Swiss army knife of text
editors" <bug-gnu-emacs@gnu.org> writes:

> When opening an org file and running imenu, the structure is not parsed
> properly. I need to kill the buffer visiting the org file and find it
> again. This only affects the first org file opened in a given Emacs
> session.
>
> To reproduce:
> ...

Org activates Imenu support only after Imenu is loaded. Effective only
in Org buffers opened after Imenu is enabled.

I tried to clarify this in the manual.

See the attached.