Safety before finish
A decorative panel should remain securely attached. If one is sagging overhead, keep the area below it clear and arrange an inspection. Water staining or recent leakage makes the situation more urgent.
Do not assume the visible panel is the only part affected. Fixings, framing and the surface behind it may have changed.
Find out what failed
A wall panel that lifts at one dry corner can be a different problem from several panels separating after damp weather. An installer needs to identify the exact product and fixing method before choosing a repair.
If there is a leak, resolve it first and allow the affected construction to be assessed and dried. New cladding over a wet surface only hides the cause.
What to show an installer
Provide a wide photograph, close-ups of joints and fixings if visible, and the installation date. Note whether the problem followed rain, cleaning, heat or a plumbing issue. Those clues help avoid a repeated failure.