Gap Opening Between Window Casing and Wall

A widening gap has appeared along the inside edge of the casing around a replacement window. It’s roughly 1/8 inch at the widest point and is most noticeable on the upper-right side, where the casing meets the painted drywall. The gap wasn’t obvious immediately after installation, but it has become more visible over the past several months.

I’m trying to determine whether this is normal seasonal movement or a sign that the trim or window opening is moving.

- Does the gap widen during colder or more humid weather, or stay about the same?
- When the sash is opened and closed, does the casing or adjacent drywall move at all?
- Is the separation between the casing and wall, or is the drywall itself pulling away from the rough opening?
- Are there visible nail or screw heads, loose trim, drywall cracks, or gaps at the window jamb?

Would you check the fastening and the drywall first, then recaulk if the movement is minor? If the casing shifts when the sash operates, should that point to a problem with the window installation rather than just seasonal trim movement?