Strange error with Aether

I have been only capable of replicating it twice on two years:
This last time it happened with Marth proccing Aether on a Corrin.
According to the pre-battle screen Marth could double Corrin, Corrin could counterattack, and Marth would have killed with the second (i suppose normal) hit. From this, all well, but I swear, the damage and HP recovery numbers appeared twice on the screen in quick succession, like if Marth had dealt two consecutive strikes and triggered Aether on both, and the Corrin didn't seem to counter-attack afterwards (the battle sped up dramatically after this happened). Marth did NOT have Desesperation and he had the Spectrum Drive-refined Falchion equipped.

I can't confirm wether or not the second hit triggered a non-damaging phantom Aether or a true Aether.

Anyone has an idea of why this happens?