SecuExtender randomly disconnecting from USG310

At my client office they are using the SecuExtender VPN Client (SSL_VPN_Client_4.0.4.0) but getting randomly diconnected without any reason. I let them use a wired connection from home and a ping logger tool (ping 8.8.8.8 -t) to be sure it is not the home provider causing disconnect issues. There is no packet loss, so the VPN itself is disconnecting without a user action.

From the SecuExtenderHelper.log file this is hapening before the disconnect:

This issue is already playing for several months, the zywall is also using the latest firmware: V4.72(AAAB.0)