Thank you for reaching out to the SE Community, my name is Jon and I will assist you with this query. I am sorry to hear about the issue that you're having with the network management card (NMC).
I understand that you are having an issue with the NMC showing that it couldn't communicate or has lost the link between the NMC and the UPS.
Kindly go over the FAQ article below as it suggests the steps that you can do to determine where is the issue coming from. It would require having another UPS and another card as you'd need to swap and/or install a card into the SmartSlot of the UPS.
I have noticed as well that your network management card's firmware is v3.5.5 which is old firmware and based on it, the card that you have might be the first generation NMC which is already obsolete. I have included the link to the latest firmware applicable to the card as well.