Okay maybe someone can/will open an issue in that Codeberg issue tracker above for Mitra and loop @pfefferle in too because I've got the distinct gut feeling that this problem is going to require an bug report at his #ActivityPub plugin's repo too, considering it appears that Mitra AND Socialhome aren't capable of responding to an #ActivityPub_Plugin powered #WordPress site with a reply to an article, and I've a sneaking suspicion this bug extends even further - probably into the space of #Hubzilla, #Friendica, perhaps #Takahe and the Pleroma/Misskey families of forks too - sad.
So just checked a couple of other platforms - This is not good - replies show up on the platforms and notifications go out to all of those cc'd but.... Poof! the replies just go into hyperspace never to be seen again - They're NOT showing up as replies / comments to the WordPress articles!!! - I'm sure more than a few #Fedizens have already discovered this the hard and most frustrating way. Yeah I don't think that plugin appears anywhere near that of a release candidate now. I'm sorry I hyped it up so much, taking the word of others without putting my fingers in the Jesus holes myself.
I'm not saying that it's not worth using at all if it only supports masto, but it's certainly not of Fediverse grade (ActivityPub) worthiness to mention if it doesn't work with most #ActivityPub powered #Fediverse servers.
I'm going to just let the powers that be attend to this matter. People get paid for this and I thought it was a well matured WordPress plugin by a salaried crew. I don't get paid for this and I do have paying work to do right now.
I guess I let my enthusiasm get ahead of me before bothering to actually thoroughly test it this time. I know for me, I won't be installing it on WordPress servers or advising people to do so until it actually works withthe majority of the plethora of #ActivityPub_Compliant#Fediverse, and not just masto, servers.
My work is done here - I really was enthusiastic about this, but that was apparently premature.