Immediately before I bought my airplane a few years ago, the owner had a uAvionix EchoUAT installed for ADSB in and out. It was a "problematic" install, done by an A&P, and was complicated by an inadvertent mis-pinning in the main harness (hard to track down). After fixing that, I still had serious trouble with ghosting. My own image would suddenly appear very close to me, sometimes right on top. I'd get altitude data (same) but no ID and no direction vector. The system would announce "traffic". Then, a minute or two later the image would disappear. Several helpful conversations with uAvionix determined that the EchoUAT antenna was mounted too close to the transponder antenna, and the coax run from the transceiver to the antenna was too long. We had to relocate both transceiver and antenna to the left wing.
That mostly fixed the ghosting problem, but not completely. I fly in a rural ADSB fringe area and still get ghosting randomly and rarely. I've been told that both the installation and software configuration are correct, and that in this area of the country it's just the nature of ADSB. When I do get ghosting, it's virtually always in the northern, less-populated part of the state where there are fewer ADSB ground stations and never in the southern part closer to Minneapolis. In those same low-beacon areas, I also usually get PAPR failures, never when closer to KMSP.