I read that some firmware on some WD Red EFAX was buggy too and caused some of the RAID building issues earlier in the year.
From limited refresh-reading some of the issue comes from having to rewrite existing data in the next track while writing new data, as the write head is wider than the read head and writing overlaps the 'read' tracks and hence shingle in SMR is like roof and wall tiles (smaller read head = more data on the same physical dimensions). I'm assuming this becomes more apparent when the disk space gets used up more. Also if a drive is managing how data is written then in RAID there may become issues between different disks.
Not a disk expert and will need to do research when I've spare time.