Terry, not that it will help to solve your problem directly, but I am seeing this same warning, and perhaps my details will be a hint as to how to solve this problem, eventually.
In my case, I was running a Carbon Copy Cloner backup of one external USB drive to another external USB drive, and accidentally unplugged the cable leading to the dock that contained the two drives during the backup. Bad move: this killed the backup, of course, but worse: After that, I was no longer able to access those two drives. I can see the drives in the Disk Utility application and from diskutil and fsck_apfs on the command line, but I cannot repair the volumes or mount them. I can add volumes to the container, but not access the container that has my data. fsck_aps from recovery mode, another boot disk, or from single user mode gives the invalid dstream error. This seems to have something to do with disk encryption, but command line things intended to decrypt did not work for me either. After many hours of working on this, I am giving up until some other clue arises or somebody updates their disk repair utility to be able to address this. Maybe a future version of Disk Utility, maybe Disk Warrior (cannot deal with apfs yet). So right now I have lost 1TB of data. My fault, of course, for adopting a new file system so early, and for converting my external spinning hard drives to apfs so early on. On the other hand, I feel that Apple might have put apfs out there just a teensy bit half-baked.
One strange thing that MIGHT be a clue: on bootup, the system asks for the disk encryption password for each of the two external USB drives, and it always asks twice for each one, but does not mount them. This does not have to do with USB as a connection method, since it happens when I put the drives in an external thunderbolt box as well.
