I exported a Guest Community group from the default (first) instance with all options checked;
Then on the same liferay database i configured a new instance and imported this LAR with all options checked into the new instance's Guest community (with the community portlet);
Results in the new instance were AFAIK perfectly imported but in the originating Instance
A lot but not all of Journalcontent reference were lost as were Structures.
NB: Importing the LAR back into the originating instance fixed everything for this instance but then the same happens to the new Instance.
I will attach my LAR