Can't add credit to episode of Heavy Rescue: 401. Copy from existing credits feature not working. Error message shown

I am trying to add an actor to an episode of Heavy Rescue: 401, but the feature to copy from existing credits isn't working. I am trying to add information to S01E05. Only 7 names are listed under existing credits for Season 1. This in itself is incorrect. But if I click through Seasons 2 through 7, it says "There are no existing values to choose from for this field."

I don't know why this is.