Hi, as you know EzVPN tunnels are not supposed to be permanent as L2L ones.
The tunnel is going to be dropped depending on the IPSec SA lifetime set on the router. If there is no interesting traffic passing by through the tunnel the SA is renegotiated and the tunnel is dropped.
I would suggested set a continuous ping on the remote location so to the other peer so that the interesting traffic is guarantee to be always passing through and the tunnel SAs can be renegotiated, hope this helps.
Armando Yesua.