Ender 3 v3 se - PEI Magnetic Flexible Steel Plate

Can you tell me if the magnetic plate that comes with the printer is coated with something (for better adhesion)? After the purchase, everything stuck to the table perfectly and everything was printed, but after a few days of work, the first layer stopped sticking. I tried changing the table temperature, calibrating, but nothing helps. I only wiped the table with a damp cloth. How can you clean such a magnetic plate? And what can I coat it with for better adhesion?