Could he please remove the ‘Certificates’ directory located here:
C:\Program Files (x86)\Steam\steamapps\common\Warhammer Vermintide 2\EasyAntiCheat
Then, proceed to repair Easy Anti-Cheat using the EasyAntiCheat_Setup executable located here:
C:\Program Files (x86)\Steam\steamapps\common\Warhammer Vermintide 2\installers\EasyAntiCheat