0.12.1
If ha_zigbee2mqtt_networkmap is installed via HACS, the file viz.js (folder name equal to file name) is missing. An archive remains from another file (full.render.js). See screenshot:

Will try to fix that to 0.13.0
rgruebel/ha_zigbee2mqtt_networkmap#18
Most helpful comment
Will try to fix that to 0.13.0