I doubt this is likely to be the case, though. Antibodies to SARS seemed to have long lifetimes (several years), and COVID is likely to be similar. It is certainly possible that for some people, immunity fades much faster for reasons specific to that person, and that may be what is being picked up in these reports.
It is also possible it's just shoddy lab work. There has been a ton of that going around lately, and it's not just caused by pressure from the situation. Not all scientists are equally competent....
(Disclaimer: my knowledge of immunology is likely little better than yours, but I did at least used to be a Real Scientist in a different field.)