I noticed that for my generated Wan-Videos no thumbnails are displayed in IIB. I then added the --generate_video_cover to the start and now IIB won't even start but creates a huge amount of errors like this in the console:

File "av\video\stream.pyx", line 21, in av.video.stream.VideoStream.getattr
AttributeError: 'av.video.codeccontext.VideoCodecContext' object has no attribute 'close'
Error generating video cover: C:\MyProg\ComfyUI\output\video\ComfyUI_00006_.mp4
'av.video.codeccontext.VideoCodecContext' object has no attribute 'close'
Exception ignored in: <function PluginV3.del at 0x00000243E2674C20>
Traceback (most recent call last):
File "C:\MyProg_GitProjects\InfiniteImageBrowsing\venv\Lib\site-packages\imageio\core\v3_plugin_api.py", line 370, in del
self.close()