IPsec renew parameter setting

I’m having a problem with the setting of an IPsec tunnel.

I successfully created a VPN tunnel (IPsec) between WR21(dynamic IP) and Cisco RV082 (static IP over NAT-T). Tunnel is up and data flows in. On this tunnel I set “Renew the tunnel after” to 2 minutes.
Then, I created a new tunnel from a different WR21 with “Renew the tunnel after” to 2 hours.
Both tunnels seemed to work fine but actually they behave in different way:

  1. tunnel 1 has been working properly without any interruption for 5 days. No VPN tunnel break, NO data flow break
  2. tunnel 2 time to time drops the VPN tunnel and it takes a while to established again the connection. Data flow is interrupted.

Any ideas why this happen?
If I keep the 2 minutes for “Renew the tunnel after” field, is there any problem for the Digi WR21 on the long rung?