SG230 in HA setup: Uplink balancing not working.

Hi,

I'm trying to get Uplink balancing working with one of our clients.

Client in question is using two SG230 units working in a HA setup. Firmware level 9.404-5.

We have two WAN lines: 

One VDSL line which terminates on a AVM FritzBox Router. This router is defined as the default gateway in the advanced settings of the ETH0 nic.

One SDSL line which terminates on a Cisco router which is provided to us by our ISP Deutsche Telekom. 

The Cisco router is connected to both SG230 units to NIC ports ETH2 using a simple, unmanaged switch. 

I added ETH0 and ETH2 as active interfaces in the Uplink balancing tab. I didn't create any Multipath rules, first wanted to make sure that automatic balancing works as expected.

And well..it doesn't! At first everything seems to be working fine, using the flow monitor I can see that there is indeed traffic going through both interfaces.

The problem is, that it only works for a few minutes and then everything is dead...no client on the network can connect to the internet at all.

As soon as I specify ETH2 as a Standby interface, everything is working fine again.

I tried numerous things, among them trying to specify ETH0 as a Standby interface which rendered my whole HA setup completely unusable since this deactivated the ETH0 interface completely...fun times, had to restore from backup since there didn't seem to be any way to reenable the ETH0 interface.

I'm open to all suggestions at this point!

Thanks in advance,

Dominik