I’m not following your problem all that well but perhaps you have an IP conflict? This is plausible because it seems like you may be trying to bring up another set of NICs.
Assuming your client is on the same subnet, you might use the ARP command to look a the arp table mapping when the connection is good vs. when it is not. If the ARP mapping changed, you might be able to determine what devices are conflicting and further troubleshoot.
James