Patch 8.20 - Yorick Ult bound to own tower

Hi, I played a ranked Yorick Top vs. Urgot. I raised the ult at my tower (about at minute 18:30). The "Mist walkers" araised around the tower, the "Maiden of the Mist" araised just beside the tower. When i pushed the lane, the "Mist Walkers" came with me but the "Maiden of the Mist" stayed at my tower and did not move! It stayed there until minute 26:00. So any thoughts?