Caulk shrinking and paint cracking

Hello,

I fitted new skirting sometime during last summer and gripfilled this to the wall. No problems there as far as I am aware.

I sealed the top gap to the wall and the imperfect end joints and joints to architrave with caulk. I left that a while to dry, I'm guessing it was probably overnight. Then undercoated and topcoated, top coat was an oil based white gloss applied with a roller.

Sometime later, there a cracks showing as dark lines in the corners. Nothing along the top of the skirting where it meets the wall.

I am guessing that the caulk was dry to touch when I painted but shrank further over the following weeks or months and eventually showing these cracks. I have been using caulk for decades, so consider myself reasonably experienced. I have not had this problem before.

To avoid this in the future, other than leaving the caulk longer to dry out is there anything I have missed? How long should I leave it to dry?

Thanks, Steve