They're all speculations, but the fact that the game was delayed before is a fact, and it might be because of development problems, or a clash of creative decisions in the game, or they've just been polishing the game. This doesn't prove that there weren't development problems and viceversa. 

Well it did get delayed, from November to April. 

There some pre reviews on Youtube, nobody reported some problems with game.

Still doesn't necessarily mean development wasn't troubled.

Delays are usually cause development problems or polish. So that isn't really nothing unusual.

Given how scarce its delay left their holiday lineup last year, Starfox Zero was probably in need of significant work. That doesn't mean it'll turn out bad, of course. You what game had an intensely troubled production? Metroid Prime.

7 years of development, if I heard right. And it really doesn't look like a game which needs so much time. Development problems is a given in that case.

You mean Starfox Zero, or Metroid Prime?

Metroid Prime, yeah. Didn't Tanabe say that the game started its development on 2009? That was the most shocking thing I've heard on the Direct. I mean, I'm not in the Federation Force looks like shit bandwagon, but it really doesn't seem like a game which would take 7 years to make. Development problems is the only option, I'd say. 

I actually meant the original Metroid Prime on Gamecube.

It has an incredibly difficult production; draconian work conditions, 80-100 hour work weeks, embezzlement of funds, key staff being kicked out/leaving and being replaced willy nilly, major layoffs...

It's a wonder it even got finished, and a miracle it turned out as great as it did.