The the Seeking Arrow Arcane Shot option of the Arcane Archer says:
[...] When you use this option, you don’t make an attack roll for the attack. Instead, choose one creature you have seen in the past minute. [...]
[...] The arrow flies toward that creature, moving around corners if necessary and ignoring three-quarters cover and half cover. [...]
And the rules on cover state:
A target with total cover can't be targeted directly by an attack or a spell, although some spells can reach such a target by including it in an area of effect. A target has total cover if it is completely concealed by an obstacle.
So does a target completely out of sight (e.g. they've walked around the corner) have total cover from you, and thus isn't a viable target? On one hand you don't have 'a clear path to the target' on the other the seeking arrow is 'moving around corners', and also you don't technically target the creature, but you 'choose' them. If the shot option completely ignored cover it would probably say something like Sacred Flame does (which is 'The target gains no benefit from cover for this saving throw.') instead of 'ignoring three-quarters cover and half cover'.
The way it's phrased, implies to me that despite going around the corners of something granting total cover, the shot fails? That doesn't seem right to me though.