Hello!

There can be several reasons for this behaviour...

Behavioural, Pica, stress or anemia (look into all of these).

I have a cat that likes to lick furniture, floors (gotta really watch which products I use), soap and my skin . Had all the tests done as I suspected anemia, but no it wasn't.... Its just something he does, when he can smell certain substances he is attracted to. 9 years down the line he still does it, but find he is attracted to surfaces treated with anything with ethanol glycol/propylene glycol which are members of the antifreeze family. REALLY toxic to cats, but they are attracted to the sweet taste/smell.

Baby wipes, body lotions, shampoos, furniture polish and cleaning products (the list is endless) contain this, so I have to be very careful what I have used when he wants to 'lick' ....

Maybe you have cleaned your walls with a product, your cat is attracted to?