Base crystal invincibility glitch?

Just played an ARAM match and when we destroyed the last turret, the enemy base was completely invincible for about 10 seconds. Even the minions couldn't attack it. Our base crystal died normally so I'm thinking it had to do with certain skills.

Not sure if Warrick's fear and suppress going off as the tower died had anything to do with it.

We had Warrick, Nami (bot), Soraka (bot), Shen, Rumble?

They had Yi, Sona, Blitzcrank (bot), Lee Sin, and the frost phoenix.