Well the first issue is specified here and will be fixed: LibreNMS and Oxidized Error page
Regarding the second issue that is more serious. It seems to be an docker DNS issue.
The logs show that it cannot get response from http://oxidized:8888, but the ping from inside the container works. It seems to be that it cannot find oxidized, but will find oxidized.librenms-network. So I changed the URL to http://oxidizied.librenms-network:8888 and it works.