Pokémon Scarlet and Violet are buggy games. This is a known fact right now for any fans of the franchise, with a new exploit seemingly popping up every week. The latest exploit seems to mess with accuracy checks in the Battle Stadium, with certain moves missing more often than normal and other moves with low accuracies having a higher chance to hit. This includes one-hit KO moves like Sheer Cold, and one Twitter user found a way to exploit this bug to make sure that this one-hit KO moves land every time. You better stay away from the stadium this time.
For some context, Reddit user u/Lord-Trolldemort was encountering strange patterns when playing S/V doubles and made a post reporting their findings. This user noted that Frost Breath, a move with 90% accuracy, was missing more often. In 14 battles where Frost Breath was the first move executed, it missed every time, which would be a one in 100 trillion chance. The conclusion from this? In the Battle Stadium, the RNG that determines whether moves land or miss is not working correctly. Ultimately, players concluded this was a case of fixed RNG, using the same RNG seed for every battle.
Users then discovered, due to this fixed RNG, that battlers can manipulate this exploit to ensure that one-hit KO moves always land. For example, one user discovered that a combo of Fake Out + Sheer Cold will constantly land if you are moving first each time. Another supposed combo is Air Slash + Sheer Cold.
Assumedly, this would work the same for other one-hit KO moves like Fissure. Other moves with lower accuracies at 90% (such as Heat Wave) should also function the same. Fortunately, players think that this issue is only present in the Battle Stadium and not in offline battles or Link Battles. However, this is something Game Freak must fix immediately before online competitive play begins to blossom.