F5 LTM manual resume problem

mwi 

So if i understand your issue is fail back not fail over.

What i believe is happening is that when you bring the "active" node back online (so both are now green) traffic is still on the "backup" node.  Now i believe the behaviour here is that the active node should start taking on new traffic, but existing traffic will stay on your existing live node so in this case the backup node until the connection is broken or timed out.
If you want the backup node to stop processing traffic, you need to find a clean way of closing the connections so they are remade at the f5 from the client.  This will depend on your application but this might not be too graceful.

You could try putting the backup node into disabled or offline modes to help with this process but if the application doesn't open and close ports regularily this may not help you. So you'll be back to working out a way that you can close the connections on the backup server so they are remade on the active server.
It would be worth testing this with your application if you have that option.