Solution:

If the Check Connection item is set to enabled or enabled + bind, it activates checking the connection to the mobile network. The router will automatically send ping requests to the specified domain or IP address at regular time intervals. In case of unsuccessful ping, a new one will be sent after ten seconds. If it fails to ping the IP address three times in a row, the router terminates the current connection and tries to establish new ones. Checking can be set separately for two SIM cards. Send an ICMP ping to an IP address that you know is still functional. If the Check Connection item is set to the enabled option, ping requests are sent on the basis of routing table. If you require each ping request to be sent through the network interface, which was created when establishing a connection to the mobile operator, it is necessary to set the Check Connection item to enabled + bind. If you mark the Enable Traffic Monitoring checkbox, then the router stops sending ping request to the Ping IP Address and it monitors the data stream on the connection to mobile network.