I think that part of the confusion on taking the "Right" or "Left" has to do with the place where pilgrims can begin their descent into Roncesvalles.
As you begin to head downhill off of the Col de Lepoeder, There is a concrete marker/post that has the red and white striped GR marking on it, and a well worn trail that is alongside that marker headed downhill. Here are Google Map pictures to show this:
This shows the road that will be the less steep and potentially slippery choice. The Camino is the dirt path to the right and you will walk onto the roadway to continue downhill.
https://www.google.com/maps/@43.026...4!1s80MV4HxNY0eXQ4WprTofpQ!2e0!7i13312!8i6656
https://www.google.com/maps/@43.026...4!1szNy_idSIAKJV77KTebNbsw!2e0!7i13312!8i6656
That is where you make the decision on which path to take downhill. You can continue to follow the road, which is why some say to choose "Left".
However.... if you take the GR path down a short way, you will again come to the road, saving a bit of walking.
https://www.google.com/maps/@43.025...4!1snNyS2Ux8LZz6RoR1Y7kSCg!2e0!7i13312!8i6656
In the Maps picture, you can see on the right -- where the red-jacketed person is -- the GR shortcut as it re-connects with the road down to Roncesvalles. To the left of the road, you can see the steeper trail to Roncesvalles. This is what folks refer to when they say to take the "right" in order to walk the less steep road downhill. But, back up at the Col de Loeper you can also see how being told to "take the left" -- in order to take that road -- are
also correct if one doesn't use the short stretch of GR trail to take a shortcut to the road further down.
It all depends on where the direction giver is referencing the starting point. For me, it is after the GR Trail shortcut. For some others, it is prior to the GR Trail shortcut.