A classic builder mistake
We come across this all the time. Dry-lining or plaster boards stuck to Wet/Damp walls with adhesive. Within a couple weeks wet patches appearing on skimmed board as adhesive becomes a conductor for the water to penetrate to internal finish as can be noted on pic on above
Also boards were stuck directly to a failed tanking system this again causing major damp problems. See pic below.
This is a costly mistake as all affected Damp areas have to be stripped. Walls treated and reinstating works can then begin.
If Dampness, Rising damp, Woodworm ,Dry Rot is suspected is suspected in your property,Building Call Advanced damp proofing for a property survey.