I can see a lot of issues coming from playing as Ciri, now that I think of it. She can travel through time and even enter different dimensions and stuff. How tf are they going to incorporate that?

My guess is that she traveled to a time where it was actually possible for her to complete the trial of the grasses, and that fucked with her ability to actually do that kind of travel to some degree. At least, that would be the easiest and probably best way to write themselves out of such a deathly corner.

I guess this is why sequels aren't necessarily good things sometimes.