Running 6.6.6 and have multiple dockers. Steps to reproduce.
1) shutdown dockers
2) stop array
3) start array
4) attempt to start dockers
Unraid will show all my existing dockers. However when I attempt to start them unraid will complain no such image is available. To work around this, I go to settings > docker. Disable dockers, apply, then enable dockers. Once completed docker images will start up properly.