A good workflow is always deleting your OC profile from hiveos before adding any new card, so the first boot with a new card does not have any oc in any of the cards. Hiveos tends to apply the previous card’s oc setting to a new card and sometimes the settings are so off that the new card could not boot at all. Booting in maintenance mode also helps.
Also, be sure to test if the rig is rock solid (a couple of days running without any errors) with 1 card, 2 cards and so on, so you can rule out any issues that are not related to the new card.