Try go into the workshop folder, pull the portrait mod outside into the addons folder and restart the game, it should work.

It's working normal if it's the 'FIRST TIME' that i'd subscribe for it, but in the other hand. These kind of HUD is not working well like if if i have to add some mod skins in l4d2 characters. Their signature HUD of the skin mods for the characters is the only one who's working not these HUD icon.