If It happen after executed the command of "docker exec pixman sh -c 'flask mytvsuper_tivimate'"?
It also happen to me, maybe because of I use sg vps to deploy pixman docker, but I try 2-3 times, and waiting a moment, and then it will generate the playlist.
Because some channels are only available to members, using a normal user's token to get the link will get a 403 error, which is not a network problem, but caused by not having a membership.