Same issue here
I have schedule to restart my Synology router time after time.
Hassio was not affected on WiFi channel, but then I decide to connect it over Ethernet directly to router got this issue too
Hassio became unacceptable with IP or DNS name in browser, but for some reason it accessible over SSH (ipv6 I suppose)
Just edit file /etc/NetworkNamager/system-connections/[config file name] over SSH with remark example provided, and it fixed my issue