Spectator link claims the room is full or it joins a game as a player
The spectator=true link tries to join the game as a player. If the room has space it will join it as a player, if it's full it will get you "Countered" because "the room is full".

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PizWiz#67822 commented
I am now unable to record and make content about MTG now that the spectate feature is gone.
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A3e#79857 commented
This feature is critical to the online tournament meta. This also enables us to share experiences with friends while not actively playing with those friends.
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spode#07710 commented
This bug also basically voids the ability to run online tournaments via spell table as the alternatives for judges to view a game for judge calls are not ideal
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AetheriumSlinky#26532 commented
Background info: we (the r/cEDH Discord) often use the spectator mode link via SpellBot to oversee games where there have been reports about misconduct to take moderation action. This feature is vital in keeping the games and the Discord server clean as per our own rules.