How to make Rotobrush work when Composition is exported from Premiere Pro?

Hi,  I've been having this issue for quite a long time in different versions of After Effects and Premiere Pro. I have a footage edited in Premiere Pro, say it's an iPhone clip in which I need to isolate a person from the background. What normally I do: I choose "Replace with After Effects composition" from the context meny of the clip, then AE opens and I open the clip monitor and choose the rotobrush and do the job. Now and then, and recently it's happening every time, when I try using the rotobrush tool on the clip in AE, tho whole image is selected, not the person or object. No matter how I draw on the image, AE selects the whole image. If I fallow the advice AE gives me - "Framerate mismatch. Set the framerate of the sequence the same as the clip" the problem disappears - I can draw with the rotobrush tool and it selects the object or person I draw on. But since the framerate is changed, when I go back to Premiere Pro with the isolated person there's a mismatch in its framerate amd the PP sequence framrerate resulting in a different  "speed" of the isolated material. How can I cope with it and why cannot AE work with PP's settings since they are linked?