EMB-170 Captain reported a pressurization malfunction during descent including erratic cabin rate of descent; which later corrected. The flight landed at the destination and the Captain insisted on maintenance troubleshooting of the system; which deferred the cabin auto pressurization system.

Narrative

Flight ZZZ to ZZZ1; during descend phase of flight around FL200 Crew awareness message 'PRESN AUTO FAULT' came up. I looked up the QRH. But then a few seconds later RATE FPM went to amber color showing -3100 even though Cabin alt was showing green. Immediately my ear felt abnormalities; so l asked my FO do you feel anything different and he said yes. At that point I felt that the something is not right with our pressurization system so I wanted to get down to a safer altitude asap and then assess the situation further before situation get any worse. So I requested for 10;000 feet; got approved. During this phase; a few seconds later everything was back in the green (no amber). I called FA to make sure everything is normal in the back there as well and the FA did confirm everything is normal back there so I did not declare an emergency.On the ground; after parking checklist; I informed dispatch and Maintenance (MX) about the situation. Maintenance asked me to run the system and fault was cleared. However i truly felt something is not right with pressurization system and I insisted MX to have this system checked out before I sign it off. He took my advise and deferred CABIN auto system.