MySQL failed on startup.
This is a very rare error. It has to do with sharing of layers (we think). So in fact, we haven't been quite able to figure it out, but we have a solution.
You have to remove the volumes for your container.
We start by removing our container. Use this script with the name of your actual container (shopware in our case).
ON HOSTdocker rm -f [containername]
Now we have to remove the volumes. Let's find their names.
ON HOSTdocker volume ls
Figure out what volumes belong to your image (by using their names) and then delete the mysql (and maybe shop) volumes.
OM HOSTdocker volume rm -f [name]
If you now restart your docker container, it should work again. It's also time to restore your clean MySQL dump, if you have a running project ;)