They appear with question marks because there are no icons in their folder. Even without the icons, the avatars should load and you should be able to play with them. If there's some of them that don't work, write to the creator of these avatars.

There are some temp files that are stored here: Program Files (x86)\Steam\steamapps\workshop\content\274920. Find the avatar by looking up its code. Each avatar has a code so to find this code look for it in the Workshop link. For example there's this avatar: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2197742359 its code is what comes after the id. Once you've found it, delete the folder and it should disappear for good from FaceRig.