This is the problem. Something is already on port 10000 when Webmin tries to start. Maybe an old Webmin installation?
Kill whatever is on port 10000, and then dpkg --configure -a
That said, it’s a bug that starting Webmin results in dpkg being in an unconfigured state. This shouldn’t happen. @Ilia @Jamie we need an || after the service start to prevent this. Installation shouldn’t fail like this just because the service can’t start. (I mean, it’s a package bug to leave dpkg in an unconfigured state like this, not merely a matter of taste.)