Are You a Human PlayThru not working

I’ve been using the Are You a Human PlayThru option for the last week and it seemed to be working fine until a day or two ago, now when I try it after I complete the game I just get sent back to the Create a site screen.

I’ve tested other options (Admin questions, cats/dogs) and they’re working fine, so don’t think it’s my site. Nothing at all in the error log when it happens.