From what I read about the EPR fiasco in France, Finland and the UK, there are always many contractors and subcontractors involved. Some delays were due to a real lack or loss of industrial knowledge and tooling (many components of the EPR are considerably larger than those of previous reactor designs) which can explain poor procurement choice, others are more easily explained by construction companies that were just not up to the task, when it's "just" faulty concrete or welding.
In Finland during construction the local nuclear safety company found reinforced concrete that had 0 rebar in it etc forcing a lot of stuff to be redone due to someone trying to cut expenses.
Though those issues happened a long time ago. The recent delays are mostly issues with the automation systems and the turbine (both subcontracted to Siemens by Areva).
But yeah a lot of the issues are the "nobody has ever done this before". The steam turbine used by these plants is literally the largest ever built.
