I consume the Kraken API to get past broadcasts for some old time streamers and over the past few days the markers endpoint has been returning null game_changes. This is unusual because Lirik changes games many times during a stream and it is only returning game_changes for a few videos.
Twitch don’t often comment on undocumented endpoints. If it’s not sending reliable data back, it’s probably because it wasn’t designed for your use, and like all undocumented endpoints it may be experimental/temporary/changed/removed at any moment with no notice.