It loads in XnView full screen mode, i press enter and it goes to thumbnails view where XnView gets stuck forever cannot load thumbnails.
As soon as i select another image XnView instantly finish loading all thumbnails.
Same behavior if i navigate into other folder trough XnView and then go back to this folder and quickly press END key on keyboard to select last image before XnView has finished loading thumbnails, it also gets stuck on the last image.
P.S. this bug only shows if folder has too many images.
Thanks to your detailed description I can reproduce