Hi
sounds like the macs not resolving to ip until traffic is sent from server somehow , the fact you see the issue on both stacks that are completely different in architecture makes me think it might be the servers
are they all running same OS , are they same model etc anything common about them
Does it only happen when bonded , does everything work without bonding on the servers
do you have any issues with pcs having same issue when connected to the switches
did you try a laptop in same port when the issue is there to see if it sees the same problem as the servers this will rule out the switches
I would check the arp table see if the server macs are resolving properly when connected and not incomplete in arp table