Testing out the latest build "giongto35/cloud-game/cloud-game:master" only player one slot works no matter what square you select for everyone connected. It seems to be across multiple emulators as well, N64 and SNES is what I tested specifically.
It works for NES, SNES games on cloudretro.io and locally (even with the latest master branch update).
Maybe your selection of games doesn't work well with a multiplayer (controller) setup.
Testing out the latest build "giongto35/cloud-game/cloud-game:master" only player one slot works no matter what square you select for everyone connected. It seems to be across multiple emulators as well, N64 and SNES is what I tested specifically.