Apparently this is still an issue though the first time I've run into it since a couple versions ago. Hiding upstairs in Mansfield like the wuss I am, I walked back and forth in the hallway to pass some time. It seemed like when I was directly on top or adjacent of where Sylvira was underneath me, she was able to cast a freeze ray and land a hit. Sometimes the next step would get one off, sometimes it wouldn't.
My necromancer is still upstairs tending to his wounds as of this writing so I may have updates :P