Export mappings do not support objects with self associations.
When trying to export an object through self association "No valid associations available." is raised as error.
A workaround is to retrieve the object by association in a microflow through "by microflow”, which is litterally the same as would happen when choosing by association directly.
"It's in fact something we never intended on supporting before, so it's a known limitation, rather than a bug.”
(Support Ticket ID 129227)