On some PC's you have to re-instate the libraries every time and on others the message comes up which if you press skip migration then the objects are there no problem.
Ok so have deleted all model elements. so nothing is left.
Which means the issue was with archiCAD migration library.
Libraries attached are 12 migration, 18 library and "older" migration libraries folder (called ArchiCAD migrations Libraries)
The migration libraries used were not from ArchiCAD 18's migration 'pack' - we use a server located library archive with everything on. I guess it has something to do with going from INT version to UKI.
I think you are right but to be sure you have to delete all elements from the file, not only the model, search all the project map (section, details, worksheets....)