Not sure what your problem is, but I just installed webmin with no issues.
$this->bbcode_second_pass_code('', 'pacman -Sy webmin perl-net-ssleay
nano /etc/webmin/miniserv.conf
#allow=0.0.0.0
systemctl start webmin')
https://pogoplugIP:10000 and it came right up.
Here is my status (a little different from yours):
$this->bbcode_second_pass_code('', '
webmin.service - Webmin
Loaded: loaded (/usr/lib/systemd/system/webmin.service; disabled)
Active: active (exited) since Wed 1969-12-31 16:43:58 PST; 5min ago
Process: 513 ExecStart=/etc/webmin/start (code=exited, status=0/SUCCESS)
CGroup: name=systemd:/system/webmin.service
ââ515 /usr/bin/perl /opt/webmin/miniserv.pl /etc/webmin/miniserv.conf
ââ645 /usr/bin/perl /opt/webmin/miniserv.pl /etc/webmin/miniserv.conf
ââ646 /usr/bin/perl /opt/webmin/miniserv.pl /etc/webmin/miniserv.conf
Dec 31 16:43:54 fluttershy start[513]: Starting Webmin server in /opt/webmin
Dec 31 16:43:55 fluttershy webmin[513]: Webmin starting
Dec 31 16:43:58 fluttershy start[513]: Pre-loaded WebminCore
Dec 31 16:43:58 fluttershy systemd[1]: Started Webmin.
Dec 31 16:45:00 fluttershy webmin[529]: Successful login as root from 192.168.100.150')