It means that the game in question uses cards that you are not currently subsribed to. That could mean
a) if it is an older game of your own, you used to have a subscription (at the time it was played) that has now lapsed, or
b) if it is a game of your own, your opponent(s) had a subscription, which enabled the card selection to come from the combined pool of cards subscribed to by all players. This could affect games that you just ended seconds ago, or
c) if it is a game by someone else, then "uses cards that you are not currently subsribed to" is all that can be said.
The reason is that while that feature is mostly used to replay some part of a game, it can be used to actually play the game, with another player or a bot, from any point in the game, including the start!
It would be nice to have a "look only" mode that doesn't allow a player to make new decisions but only had "back" and "forward" buttons. That mode could then be made available to everyone, but unfortunately, it doesn't exist.