The plaster coving strips have a threat of water damage if there are leakages in your walls or if there is a drywall problem. In such cases, it is best to seek professional help and get the wall fixed.
In some cases, it is possible to restore the coving by filling the cracks, sanding the uneven surface and paint the strips. If the material is substantially damaged, you will unfortunately have to replace the coving material with appropriate substitutes.
If the room is prone to damp and humidity, choose one of the more resilient materials (e.g. hardened polyurethane) to avoid future damage.