When sorting the videos in this channel by Most popular there are only 7 videos: https://i.imgur.com/9rnCAyJ.png
But when sorting by Date added (oldest) there are 8 videos: https://i.imgur.com/T1TGQHP.png
Same for sorting by Date added (newest): https://i.imgur.com/hf4x8jo.png
Is this a bug in the YouTube UI?