Sometimes it doesn't recognize when references/sources are the same because their url/host is different. e.g. The effect of hand hygiene promotion programs during epidemics and pandemics of respiratory droplet-transmissible infections on health outcomes: a rapid systematic review (Sep 2021) https://bmcpublichealth.biomedcentral.com/articles/10.1186/s12889-021-11815-4 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8467175/