I wrote the template that pulls in the Official Docker Container from PiHole. I swapped over from my unofficial one a long time ago that that a fully supported version could be distributed. Make sure that your repository for pihole is = pihole/pihole:latest and not the old diginc repository.
If you use the latest tag, you should have v 4.0.0-1. The release tags are here: https://hub.docker.com/r/pihole/pihole/tags/
The last update to the docker image was 12 days ago. Apparently you should not do an update within the docker image (that was what diginc said - although that may have changed)
If you have a problem with the docker image, you should ask about it here: - https://discourse.pi-hole.net/ or on the github here:- https://github.com/pi-hole/pi-hole/issues