Use the caulk. Be very neat then repaint the molding.

We've always just used paintable caulk for these types of things. If you are careful and neat, it will require minimal paint touch-up.

Wait till spring and see if it closes back up. If you caulk it and it moves backs in the spring you'll have caulk sticking out.

When we had our kitchen redone we had a few hardly noticeable areas where the crown molding was not flush with the ceiling. Our carpenter sailed he would not caulk those areas as it would create the problem you have. He never caulks slightly uneven crown molding. I think he it right too❣️

Thank you for the advice.I'll wait until spring to see if it moves back. If not, I'll get to caulking.

Add a humidifier to your home’s HVAC system. Wood shrinks when it’s dry, and swells when it’s humid.