Migration from Lotus Notes is always horrible. In 2011 I worked on many migrations to Google Apps for Business (GSuite, Google for Work etc) and there was only one person in all of Google who understood Lotus Notes and could maintain the migration tool he had created.
And every time a big user moves away from Lotus Notes (and other such dinosaurs, such as Cobol), it gets harder as this knowledge becomes more niche. The people doing it spend the rest of their career at that combany and that's it.
