As I suspected, the PCo Agent was configured already in DEMAND cache mode. However one thing changed between the PCo versions.
While using PCo 2.1 & 2.2 you had to type there the mask as you want the tags filtered (i.e. "*Code" for filtering out all tags not ending in Code) the present approach is to type the whole mask request (i,e, tag='*Code' for the same result).
Anyway, now it's working and everyone's happy!
Many thanks,
Paul