Rian Johnson offered his warning through his official Twitter account, where he somewhat teasingly also announced the release of the film's newest trailer. Though the director does clarify that nothing is spoiled by the newly released trailer, he states that the new moments that are put on display are 'best experienced for the first time in the movie'. You can see exactly what he said below.
"New #knivesout trailer ahoy! As always... it doesn't spoil anything But it shows plenty of new moments that are best experienced for