Well, it is an in-service, combat-proven aircraft, and this problem is the type of thing that often cannot be found until after the aircraft has been in use long enough for such defects to start to show.
An aircraft that has been only in limited use (F-22, Typhoon) probably has some of these "glitches" still undetected... waiting for a few hundred more flight-hours on the airframes before they appear.
Basically unflown aircraft (F-35) are even more likely to have these hidden flaws.
Therefore, the F/A-18E/F really is a lower-risk option.