Unicel filter, no back pressure???

Just installed a new unicel filter cartridge and, for the first time in 14 years, my pressure gauge indicates no increase in pressure (compared with the pressure, 15 psi, when no filter is installed). I seem to remember an increase of about 5 psi in the past.
It seems the gauge is not faulty, because closing off either the spa or the pool jets increased gauge pressure by 3 psi.
The cartridge does not seem damaged, Not collapsed, for example.
When I inquired of my local dealer, he said he had never heard of such a situation, and had no idea how to proceed.
I failed to find a phone number or eMail address for Unicel. Perhaps they would tell me whether I have a defective cartridge. Or perhaps I have a counterfeit cartridge. Or maybe (a miracle if true) they have some new kind of filter technology which produces no back pressure.
Any suggestions as to how to proceed?
StumpedInFlorida
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