What I describe below applies to APFS sparse disk images only — ordinary APFS volumes (e.g. your SSD startup disk) are not affected by this problem. While the underlying problem here is very serious, this is not likely to be a widespread problem, and will be most applicable to a small subset of backups. Disk images are not used for most backup task activity, they are generally only applicable when making backups to network volumes. If you make backups to network volumes, read on to learn more.
The title clearly qualifies the claim: "MacOS may lose data _on APFS-formatted disk images_"
I didn't know there were APFS-formatted disk images (new in 10.13). Even when you consider the many different kinds of disk images that macOS supports, there's a pretty clear distinction between disk image and a backup of your startup disk, made to another partition in another drive.
Any additional clarification would get into "MacOS may lose data on APFS-formatted disk images (disk images, not disk-to-disk, as in another volume..." territory.
A lot of people do make backups to disk images though, especially techies. I believe that remains the only method to use 'time machine' with a generic network connected device rather than an apple branded 'time machine' device? The last place you want an unreliable file system is your backups!
Not the person you replied to, but I want to make a case for ZFS on a generic small motherboard. You wind up with Linux or FreeBSD so it's a general-purpose server, unless you want to use something like FreeNAS. And with ZFS, you get snapshotting, RAIDz, checksumming, etc, as opposed to "oh it has RAID 5 woohoo".
RAID (including the software RAID in Linux) doesn't actually do checksumming for file verification. AFAIK, ZFS is the only open system to do so.
People can have opinions without them needing to be flagged as having hidden agendas. And I have worked at Apple and can assure you that there isn't some payment structure for posting on forums.
What I describe below applies to APFS sparse disk images only — ordinary APFS volumes (e.g. your SSD startup disk) are not affected by this problem. While the underlying problem here is very serious, this is not likely to be a widespread problem, and will be most applicable to a small subset of backups. Disk images are not used for most backup task activity, they are generally only applicable when making backups to network volumes. If you make backups to network volumes, read on to learn more.