Hi @Sturlae, welcome to the Sonos Community!
I’m sorry to hear that you’re having issues with YouTube Music on Sonos.
I’ve had a look into our internal information and it says our general limit is 10k tracks per Sonos playlist, and music services seem to have a 3k track limit per playlist. I don’t see any mention of a 50-60 song limit on our end, nor can I find any community posts, but if this issue was mentioned scarcely within six years, then that may explain why I can’t find anything.
The only known issue currently is where YouTube Music on Sonos doesn’t show more than 500 entries of uploaded content per container (e.g. it’ll only show 500 tracks per playlist), but this doesn’t seem like what you’re experiencing.
Are you able to provide screenshots of the imported playlists and how you’re adding them to Sonos, as well as a diagnostics after you import the playlist? If this is a new issue, then the screenshots can help when I reach out to our engineering team to request more information and additional help.