When working from home using an IPsec VPN connection from your computer to the company router you may experience the IPsec VPN tunnel failing to come up. This will occur if the company router has multiple incoming WAN connections which are configured for load balance mode.
IPsec VPN creation starts from UDP port 500 and will move to UDP port 4500. Since two ports (sessions) are used, the gateway router may regard the VPN connection as different NAT sessions and try to Auto Load Balance. This may result in the two UDP connections coming in through different WAN ports resulting in VPN connection failure. The solution here is to disable the Auto Load Balance feature for the LAN IPsec traffic to avoid the IPsec VPN failing.
In the latest firmware, DrayTek Vigor Routers support disabling Auto Load Balance for specific traffic via the Advance button in WAN >> General Setup page.
To do this enter the IPsec VPN ports as shown below, then the Vigor router will not Auto Load Balance for VPN packets.