Mobilizon Group's Invite to Mastodon Account Disappears

I was experimenting with sending messages between Mastodon accounts and Mobilizon accounts which worked as expected. I then tried to invite those Mastodon accounts to join a group on my Mobilizon instance. The list of members in the group shows them as both invited and with proper avatars, however I don’t see anything on Mastodon (feed or DM) or to the email of the Mastodon accounts that show the invitation. Is this a bug or do I need to do something different on my end? Are these two invited accounts somewhat stranded (e.g. now way for them to finish registering since the invite was lost and no way to uninvite them)?

Not in Spam. Are you able to invite a Mastodon account? Did the invite go to their email or as a direct message on Mastodon?