A couple of weeks ago, a group of South Koreans tested positive again for the Coronavirus after recovering from it:

By Friday, Korean health authorities had identified 163 patients who tested positive again after a full recovery. The number more than doubled in about a week, up from 74 cases on April 9. Those patients — just over 2% of the country’s 7,829 recovered patients — are now back in isolation.

NPR: In South Korea, A Growing Number Of COVID-19 Patients Test Positive After Recovery – 17 April, 2020

However, new reports indicate that these were false positives:

South Korea’s infectious disease experts said Thursday that dead virus fragments were the likely cause of over 260 people here testing positive again for the novel coronavirus days and even weeks after marking full recoveries.

Oh Myoung-don, who leads the central clinical committee for emerging disease control, said the committee members found little reason to believe that those cases could be COVID-19 reinfections or reactivations, which would have made global efforts to contain the virus much more daunting.

“The tests detected the ribonucleic acid of the dead virus,” said Oh, a Seoul National University hospital doctor, at a press conference Thursday held at the National Medical Center.

The Korea Herald: Tests in recovered patients found false positives, not reinfections, experts say – 29 April, 2020

This is good and promising news. The world of transparent science marches on, continuing to learn!