What’s causing this?

A year ago we had this room professionally decorated with good quality paint.
At the time the decorator struggled applying the paint to a small section of the chimney breast. After several attempts of rubbing off and repainting, it stuck, but only for a few months.

Any ideas please?

Damp/ condensation caused by either/combination of cold air on the other side of the chimney breast and the presence of salts in the brickwork from the products of combustion from when it had a fire in it.

Is the chimney still used, if not is it ventilated top and bottom?

A slow forum causing duplicate threads?