In case of Check playlist URL Please add m3u file again then turn the TV off for 2 minutes to clear TV cache then turn the TV on.
Additionally, try reducing your playlist size by removing channels/movies (especially if you have LM series LG TV with limited memory). If your playlist doesn't appear on TV or disappears after restart, try checking Save online box, when uploading the playlist. You can also try resetting Smart HUB or turn your TV off and on to clear the TV cache if you have Samsung TV.
TVs have limited memory available for app storage, so if your playlist is too big (~5 Mb), it will fail to save in TV's memory.