They don't exist.
And that's surprising given the number of people who use the idea. I wonder what psychological phenomenon they're really describing. Because, aside from pathological cases, those times in your head where a judgment function and its perception mate of the same orientation are full steaming ahead, damning other orientations into non-consciousness, are their periods of highest and best functioning. They're doing what they do most constructively.
What people most often seem to mean by "loops" is some condition where you get too much of a good thing. You over-subscribe to some one orientation. Well, newsflash, and send this one to the red phones of all the nations, everyone always does. Any obvious introversion is you manifesting some interesting in the inner world at the expense of the outer. And likewise, if you're being extroverted at all, you're stabbing the inner world in its barely beating heart for giggles.
Of course there genuinely are people who're leaning so hard on one orientation that they literally can't consciously access the other. As well there are people who lean not that hard but heavily enough that when they do attend to the opposite orientation, they do it inadequately. Now, the former is probably pathological. Certainly it sounds sufficiently unbalanced that the personality will be at least half made up of reactive or even dangerous elements. I'm just making this up, though, I wouldn't know. The point I'm more interested in though is that the latter is presumably what people really mean when talking of loops. But the thing is, it's automatic that any function lower in the order than the one you prefer is attended to inadequately. A lot of the time you don't attend to it at all, it just chugs along by itself, sometimes feeding off the scraps you send down to it in its unconscious hole. You just do over-subscribe to dominant functioning at the expense of lesser functioning.
The real "loops" condition is when you've passed through some vaguely determined border area from healthy imbalance into the degenerating. There is healthy imbalance, btw. It's where functions of the same orientation are drawn together, doing their best work, and this is at least partly available because other orientations and contents are positively excluded. However, there is also unhealthy imbalance. Where functions of the same orientation are having at it over and over but there is at the same time no contribution made to or from other-oriented content pools in some timely or appropriate fashion, then the standard of that best work slips over time. It becomes "best available" thought rather than best thought for realz.