Can you not glue and clap? Probably won't hold forever I guess.
I think you have a case with manufacturer.
Everyone knows wood is a living moving product and splits happen. Normally they just replace having factored in failure rate.
Start with a warning letter regarding small claims.
Then file...
320 grade sanding sponge.
They don't last long as clog up but that's just how they are.
Go easy so you don't affect the moulding.
Forgive.
If that's your primer that you applied you need a better application technique.
Your going to go around in circles otherwise.
If you are struggling try a...
Scrape off.
Old emulsion under. Bit powdery?
Here we use gardz to penetrate as and bind surface.
Make good with filler and paint.
Get up in loft and add more insulation so the ceiling dont get cold which will reduce or even stop condensation forming on the surface.
Or fit plastic panels to ceiling
Internal plaster?
Options...
Plastering mesh 100m x 1m rolls. Used along with multi finish plaster.
Fibre fuse rolls layed over sprayed on plaster covering walls.
Wallrock lining paper 1m wide run horizontal I have done it with smaller roll along the top.
Only 2 joins to deal with that way
Check outside drain gully. Rain water can get through cracks in drain capture and get under the house.
Make sure all the water in all the drains goes down and away as it should
Never put panels at the back of a wardrobe because the wall doesn't get air movement and heat from the house and condensation forms behind.
Could be that.
Cut a hole and look behind side panel to confirm
Sound travels through solids.
If you had foam with metal sheet then foam suspended in the air then sound won't get through as the metal will move in between the foam canceling out the noise.
Foam don't block noise but allow the solid to move (plasterboard) which will create a sound barrier.
If...