An added liner may obstruct openings, trap spills or change the arrangement intended by the manufacturer. Check whether the model permits liners before covering shelves, especially where gaps are part of the air path.
What the observation tells you
A smooth mat can make a shelf easier to wipe but may extend beyond its edge or bunch up behind a drawer. That can stop a drawer seating fully or hide liquid that would otherwise be noticed. A liner advertised as suitable for refrigerators is not confirmation that it suits every internal layout or shelf material.
A useful next step
Keep permitted accessories within their intended boundaries and avoid covering vents or drainage channels. If uneven cooling or moisture started after a liner was added, note that timing and remove only the user-removable accessory as appropriate. Do not modify the fridge itself to accommodate an aftermarket mat or shelf insert.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.