The backup failover from ADSL to 3G/4g SIM not working (3G/4G SIM working as primary routing is fine). Followed instructions in setting up Network->Internet to 3G/4G as enabled with Dual Detection set to both IP address (8.8.8.8) and DNS (a.root-servers.net). If forced to failover, WAN interface shows Internet status as Connected, but there is no connection. The Basic page shows Intenret connection is 4G.