Disk Utility Can Only Check Backup Disks in Recovery
The most serious problem with Disk Utility remains its manifest inability to run First Aid on some volumes and containers, in particular Time Machine backup stores. This problem persists, although currently it now seems confined to APFS backup volumes.
[…]
If you need to run First Aid on an APFS Time Machine backup disk, the only methods available are to use Disk Utility or
apfs_fsckin Recovery Mode. This is a serious failure, particularly as the message given to users is to “back up the data on this volume”, which is wholly inappropriate for a backup volume, and gives the false impression that failure is imminent.[…]
Less serious, but more confusing, is a sporadic bug which displays bizarre results after a disk has been erased, or partitioned into two or more containers.
I run into this last issue a lot. Sometimes partitioning fails for no apparent reason. Other times, Disk Utility says it succeeded but displays a completely different partition structure than what it had been asked to create.
Previously:
I've said it once and I'll say it again... APFS sucks!