Did the Undaunted event run smoothly on PC NA servers ?
Can we assume that they run the exact same software on both PC EU and PC NA ?
If so the conclusion has to be that it's all about the server and nothing but the servers can't handle the amount of players and has to be upgraded for this to be fixed.
If it is the servers that are not able to handle the load what are they investigating everytime the servers are overloaded ?