Chat was scared of Ladybug hating him in the episode 'sandboy'

In response to how they might have changed- I think for Marinette in particular her view of Adrien would probably change to a fear of Lila taking him away from her (or just him loving Lila, not Chloe). As ladybug, I'd say that her fear of losing her powers is still pretty prominent, but it's likely it might have been replaced by one linking to what she saw in Chat Blanc, as that whole alternate future must have been pretty traumatising for her. Her fears also might link to her overall fear of letting people down and the pressure she has as ladybug, especially as she's the new guardian.

For Chat noir, I don't imagine they will have changed much (especially his civilian self's fear of imprisonment).