please take a look at Youtube Playlist Limit?
The problem in question seems to be related to Vox caching the API response forever. I have encountered the same issue. I created a dummy playlist with 2 items, loaded it to Vox, removed it. Added 2 more items and loaded again, but to no avail, it seems that the content is cached, and that no amount of cache clear command , Vox restart or computer restart resets it.
For example, the playlist https://www.youtube.com/playlist?list=PLPX6lu9kG1JVr_cpyMhXsYsehYfFx9hB_ has 4 items, but if i add it to Vox and then add another item. When i try to load the stream again, it will only add the original 4 items and it will not see any of the new items.
If i add the stream from another computer, it is loaded properly. So this is most definitely not an API issue like stated, but a caching issue.