Wireless Dual Band AC 7620 Card in NUC D54250WYK

I added this Intel wireless card into a NUC as per above and can only connect slowly at less than 10Mbps to a 300Mbps Dual Band WAP that other computers connect to at over 150Mbps at twice the distance (I am 5 meters from the WAP and line of sight - no obstructions). Something is just not right. The card connects at 150Mbps and instantly goes down to less than 10Mbps.Does anyone have any thoughts please?