https://wccftech.com/western-digital-introduces-the-red-plus-hdds-using-the-plus-branding-to-specify-which-hdds-use/

Western Digital was among the hard drive manufacturers that had begun to using SMR technology in NAS hard drives without any notice or press releases. While this was most likely done in an attempt to cut production costs, but this has lead to many issues for users that utilize the Red HDDs in RAID or ZFS operations. Western Digital has announced a new WD Red Plus series that only uses CMR technology while the RED HDD series now all uses SMR technology.

Western Digital originally released a statement back in April that showcased which drives from each of their HDD series uses the slower SMR technology. This statement showed that more than the Red series of HDD had been using the slower technology, but the main issue for many users is that the slower performance had been affecting their RAID or ZFS technology.