If I have more than 9 video files in some folder,Pot Player will only list 9 in the playlist. I have to manually add other files This is a long standing bug (for years)
How are you adding the files into Potplayer? For me I just Ctrl + A and Drag and drop the whole thing, or you can drag the folder into Potplayer and that should show all videos.
If some aren't showing possibly Potplayer doesn't detect the format, you can probably try amending those files properties to default play with Potplayer test 1 and see if that works
Additionally, when I drag and drop new files to the playlist, list order is messed up
This can be fixed by Right click -> Preference -> Expand the Playback option and go to Playlist, then check the box for "Sort dropped files before adding to list"