Captain reported suspected false conflicting traffic indications from the TCAS and ADS-B systems. ATC stated they observed no traffic and this was consistent with other reports from this area.

Narrative

While descending via the DDUNN5 Arrival into APA; we received a TCAS traffic alert. The TCAS system showed a traffic target no more than a quarter mile in front of us at the exact same altitude and heading. It mirrored all changes in flight path that we did. My partner decided to query the air traffic controller on whether there was truly traffic directly in front of us. ATC stated that he did not indicate anything in front of us; and that they had received multiple reports of aircraft receiving the same indication in that area and typically cleared up once coming near the Denver Class Bravo. The controller requested the ADS-B manufacturer name. I wasn't able to find it immediately and offered to call on the ground; at which point; ATC advised they no longer needed a manufacturer name. Given that the indication fell within the exact geographical area that Air Traffic Control has had multiple reports of the same exact indication; I felt it was not a malfunction of our system. It was a known problem in that area. We continue the flight and landed safely. It would probably be worth looking into what is going on in that area. It is not good to be in the habit of accepting TCAS indications as erroneous until proven otherwise. It would also be worth making a note for any airports; utilizing that arrival to be aware that that is a possibility until ATC corrects the problem.