[GAMEPLAY] Spells go through Ashe

While playing against an Ashe as Nautilus, I noticed that my Q and Ult occasionally didn't affect the enemy Ashe at all, even when they clearly should have. there was literally a rope through her chest or an explosion under her feet, but nothing happened to her.
A friend spectating reported that she also ignored a Nunu Q, and that my abilities definitely should have affected her. If it was just the Ashe or if her support, Nami, helped with this, I'm not sure.

Steps to reproduce:

1. Have an Ashe and Nami on one team, and be anyone else on the other.
2. Have Ashe activate a passive of some kind. Not sure whether it's a Nami thing (E or passive) or Ashe (Q activation)
3. Use a spell or ability on Ashe
4. nothing happens.