Go into the settings for the tunnel in each router and expand the Advanced options at the bottom of the screen. You will find an option to enable Keep Alive. Turn the Keep Alive option on for both routers and see if that makes any difference for you.
Also verify that you have the latest firmware on both routers which should be 22.214.171.124 for v2.
WRVS4400N does not support Dead Peer Detection. It will reconnect the tunnel when it sees packets that need to get on the tunnel. If you need the tunnel to stay up all the time, you could have a PC making a continuous ping to another PC accross the tunnel. Other Small Business routers such as RV042 and RV082 support DPD and Keep Alive, which can keep the tunnel up.
This could be irrelevant to your situation but I am just suggesting it, sometimes the tunnels go down because your WAN ip address lease changes or needs to be renewed. While this process happens with your ISP the tunnel will go down, and in certain cases your ip could possibly change until it re-associates usually requiring a manual reconnect from the routers interface. If that is the case you could find out if you could get static wan IP addresses on both sides or consider registering with a DynDNS server to do the tunnels in that fashion instead.
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