a problem that I had to "fix" but I'm not sure about was that all instance models are invalid (unknown 'id' attribute). To get them to open without errors I had to rename all 'id' attributes to 'identifier' with a text editor.
Was the metamodel perhaps changed without co-evolving the model instances? I got both version of the projects from the gihub repo.
Yes, the old Github repo was archived in a state where the metamodel was already changed, but the instance model was not yet updated.
In the viatra.examples repository, the instance models have been updated already.