Last week while enabling Two routers with one Home Network, I forget to update the mapped IP address to my Home Assistant. After the switchover of the IPs based on the Main router, I lost the access to my Home Assistant. The following approach resolved my issue and came in handy.
ha > network info
ha > network update en3sp2 --ipv4-method auto --ipv6-method disabled
For more reading, refer the following thread at the Home Assistant Community forum.
ha > banner