I'm trying to use a previous island as a starting template

hi @AtAshTag ,
The main thing you face is the new Use Legacy Detail Mode.
UEFN Use Legacy mode after 30.00

This seems complicated but this appears for any Island 30.00 or before has these scattered around Island that were in 29.* “We hit a Road Block” error in Fortnite.

Many developers dont want to start again as they copy the template from a previous version.

My advice is start from a new version and import all your assets.
Look at 32.00 Verse has been upgraded from Version 1 to Version 2 and thats in the template
Looks like FN Creative 1.0 has been made legacy.