Something similar has been reported from China (IIRC). Maybe other places too?South Korea is reporting that 91 patients have tested positive again after having been thought cured of the disease.
As before there are a few possibilities:
1) False negatives (or presumably false positives, although I guess that is not as likely)
2) Re-activation of the virus
3) Reinfection.
The latter would presumably be the most worrying, if true.
https://www.reuters.com/article/us-...patients-testing-positive-again-idUSKCN21S15X
False negatives (and false positives) are certainly going to happen; no test is perfect, even if applied twice. I guess that in time we'll have a good handle on the distribution of false negatives/positives, by many a variable.
At a practical level, it would seem that continuing to put a lot of resources into testing would be prudent, coupled with doing a sterling job of contact tracing, and isolation.