I wouldn't say it's low fat that's directly taking you out of ketosis, but the potential converse increase in carbs that may be doing it.

This graph comes to mind, from The Art & Science of Low Carbohydrate Living:



Basically once you start to run low on body fat to lose, you need to increase your percentage of dietary fat to compensate. If you just eat a little more of everything instead, the carb creep may be enough to take you out of ketosis again.

I hit my goal about 11 months ago but have put a few pounds back on since then, which I also put down to eating a little more of everything instead of just eating more fat. Never mind, we live and learn.