Does the Arcane Archer's Piercing Arrow pass through Walls of Force and Forcecages?

Question

The following is within the scope of Dnd Adventurers League play.

The Arcane Archer martial archetype of Xanathar's Guide to Everything alllows you to select the "Piercing Arrow" Arcane Shot option :

You use transmutation magic to give your arrow an ethereal quality. When you use this option, you don't make an attack roll for the attack. Instead, the arrow shoots forward in a line, which is 1 foot wide and 30 feet long, before disappearing. The arrow passes harmlessly through objects, ignoring cover. Each creature in that line must make a Dexterity saving throw. On a failed save, a creature takes damage as if it were hit by the arrow, plus an extra 1d6 piercing damage. On a successful save, a target takes half as much damage.

The Forcecage spell (box option) says :

[…] A prison in the shape of a box can be up to 10 feet on a side, creating a solid barrier that prevents any matter from passing through it and blocking any spells cast into or out from the area. […] The cage also extends into the Ethereal Plane, blocking ethereal travel.

The Wall of Force spell says :

Nothing can physically pass through the wall. The wall extends into the Ethereal Plane, blocking ethereal travel through the wall.

Does the Arcane Archer's Piercing Arrow pass through Walls of Force and Forcecages (box option) ?

It seems to be a situation in the likes of "unstoppable force meeting unmovable obstacle". It says it ignores cover, which those 2 spells provide, but its flavor text mentions an ethereal quality, which may or may not be relevant (since the spells normally block ethereal travel). I don't know if the right answer is "it works", "it doesn't work", or "DM Discretion".

Answer 1

Both Forcecage and Wall of Force blocks Piercing Arrow.

Both effects block physical objects and ethereal travel.

Physical's definition includes "having material substance", which Piercing Arrow specifically states it is not because it is ethereal. Ethereal means immaterial, as in lacking matter.

Both effects limit bypassing the wall through the Ethereal Plane and via ethereal movement. Piercing Arrows' effect does not state it travels through the Ethereal Plane, but does say the attack has an ethereal quality, meaning that the projectile would be moving ethereally.

Both Force Cage and Wall of Force prevents ethereal movement penetrating it, and Piercing Arrow is an attack involving a projectile moving with an ethereal quality. Ergo, both effects prevent it.