When I logged into the Cockpit interface to Nethserver, there was a warning that one of the DNS servers was not responding, so I looked at the Network config. I don’t think the DNS not responding is related to the following bug, but it was the reason why I looked at the WAN config, and the warning disappeared after the various operations I did described herein.
From the Network panel in Cockpit, I selected the Configure button on the WAN interface, clicked the Next button, then Configure on the next pane.
I made no changes, but selected Nest and Configure.
Uncaught TypeError: Cannot read property ‘length’ of app.016b4eb3.js:1
at Function. (nethserver.js:108)
at s (cockpit.min.js:963)
at n (cockpit.min.js:881)
Repeating the process produced the same error.