according to this, the snap.seeded is just a flag used to signal that snapd does not work yet.
From a few threads on askubuntu it seems that sometimes snaps does not initialize correctly first time and it’s needed to either restart the computer or even install the hello world snap so that the core installation finishes. Never happened to me but not unthinkable nonetheless.
If the OP don’t need snapd in his containers, he could just create a new image with a container from which snapd had been uninstalled.