Overnight I started receiving frequent WARNING messages in the CLI as listed below. Now my node 580850 is no longer listed in the portal node list as a registered node.
In my case, with a deeper look, it was the ISP had been preforming infrastructure changes/routing upgrades and persisted at random over a month.
It seem to help to use external DNS in my router for WAN DNS #2/3
But I since removed it when I upgraded router, since it was just old, but I preferred to have anything with DD-WRT as I had been using where I can have more explicit control.
So, for whatever all that may be worth to someone later down the line… there it is.