When Photon Emperor is sent to the GY and its effect triggers, an error message appears instead of effect confirmation
Bug reproduction steps
Send Photon Emperor to the GY with a face-up Galaxy or Photon monster on field or in GY.
Screenshot OR error code
Should be prompted to special summon Photon Emperor from the GY
What OS are you using
Arch Linux 64-bit
Try this again; go online if it still doesn’t work