Hi,
For me I have two WAN connections, one is 4mbit/s and other is 10mbit/s I set the 40 as Wight for 4mbit/s and 100 for 10mbit/s. WAN Failover is configured and added both the WAN links for test.

Testing:

In the WAN Balancer, if I specify one subnet to always user 1st WAN Link, and tracert external websites or IP, the next hope after the default gateway always shows 1st Link is the one which is used. www.whatismyip.com shows correct external IP that belongs to 1st WAN Link.

If don't specify anything in the WAN Balancer or if I disable the rule which I made, the outbound connection always goes via the higher WAN Link which is 10mbit/s which got 100 as wight.

Do this test and let us know the result...

Beside that, I disabled the QoS which will gives me a real result of the outbound connection.

Hope it helps.

Thanks,