If players thought the gyms beneath them, it could explain the poor performance in them. They just did get up for the games.
Even if the players didn't think the gyms beneath them, going from a packed 18K arena to even the packed Kennel or SMC gym is a big contrast with noise. When gyms are small and empty you hear everything and that can throw one off. Even full smaller gyms can throw players off mentally when used to big crowds.
Our boys performed well in Vivint Arena even when it looked empty. Likely because depth perception of hoop to stands is more similar.