Thank you for the bug reports. You are correct that Fuwawa and Mumei are the default placeholder sprites, and will show if the cards failed to load (note that the second card slot is the currently selected card, not the enemy card). I will look into what is causing it, though any additional information you may have would be helpful, if you can spare the time. Did it happen in single player, and/or in multiplayer? Were you host or client? Did it happen when starting new games? On rematches? On new rounds?
As for the crashes, did they occur after specific actions? Were you playing on desktop or via browser? There may be some crash info at this directory: %USERPROFILE%\AppData\LocalLow\GreyManedLizard\HoloWho\ (copy-paste the path into the windows explorer bar). If there is, please send me the player.log file(s) to greymanedlizard[at]outlook[.]com. Thanks.