This issue was resolved by updating to the 20.8.4 firmware and related driver.
Running Windows Server Standard 2012 (non-R2) with the latest Windows updates and Broadcom (QLogic) BRCM GbE 4P 5720-t rNDC network firmware and drivers (20.8) and, under heavy network load (backups), we routinely get the following:   Log Name:      System Source:        b57nd60a Event ID:      16 Level:         Information Description: Broadcom NetXtreme Gigabit Ethernet: Ndis is resetting the miniport driver.   Network cables are known to be good.  How do we resolve? Thank you.
Broadcom NetXtreme Gigabit Ndis resetting miniport driver