The bot gets its data from https://lemmyverse.net - which isn't aware of https://walledgarden.xyz. I don't know why, but there's a problem with the site that might be related - if you do curl -i --header 'accept: application/activity+json' --location https://walledgarden.xyz/ it errors with 'transferred a partial file' whereas it works for any other Lemmy server. It must have worked in the past though, 'cos I was able to subscribe and post to a community on there not long ago.