morel, the error was on the child Claire. In the relationship tab the parents was listed as unknown even if you visually in the tree did see a connection, so I just reconnected her again.
This might happen sometime when the only connection was to a profile that had been merged into another profile and the merge has been interrupted somehow.
You could probably have solved it by resolving the data-conflict on the mother, where that connection probably was.
A general advise is to look for data conflicts when you have mysterious problems.