No problem. moved.
Have you specify the source IP when your configure each node?
Looks like lslb has problem connecting to all backend servers. could it be a problem with NIC port, switch port? If you use dedicate connection communicate with backend servers, you can check the packet loss of that specific NIC.
LSLB uses persistent connections, while nginx does not, there could be more ESTABLISHED connections with LSLB. Is there a firewall between LSLB and web servers?
If you do think it is a LSLB bug, could you strace lslbd while the problem is happening to help analyze the cause of the problem?