1. Please verify that the server 10.8.251.187 has a return route to the IP Pool on Syd Firewall. Run traceroute on it to see where it goes.
2. Please verify that the Mel VPN is NOT active on the remote user's laptop at the time of the test and that there are no residual or static routes present on it that may skew the test.
3. You have common VPN community servicing both gateways for the same destination. Is that community configured as MEP (Multiple Entry Points)?
4. The logs you are looking at may be filtered, please remove filters if any present.
5. If the community is not a MEP, consider creating a separate community by cloning "Remote Access" and creating two sets of rules for VPN with target gateways defined in each rule.
6. Your 10.0.0.0/8 route is too broad and includes your IP Pools. It'd be cleaner to have a different range for Remote Clients, such as 172.16... or 192.168.255... (just NOT 192.168.0.0 or 192.168.1.0).
7. Check if your Syd "CP_default_Office_Mode_addresses_pool" or whatever network you have defined for it is NATed to hide behind gateway. Compare to Mel.