When changing the E810-XXVDA2 port speed from 25Gb to 10Gb with auto negotiation off, Ports still work at 25Gb
When checking Ports speed using Ethtool or Ethernet Port Configuration Tool, only 2x25Gb configuration is visible for E810-XXVDA2 and 4x25Gb configuration for E810-XXVDA4, which is is expected behavior
Since the transceiver is in the modules and not on the card, the actual speed is determined by the modules used
Resolution
E810-XXVDA2 only has the 2x25Gb speed configuration available.
The speed can be determined by the optic modules
Use10Gb Optic modules in this adapters if you want to ensure only 10Gb speed