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Mastodon not federating to Lemmy?
(lemmy.ca)
A community to talk about the Fediverse and all it's related services using ActivityPub (Mastodon, Lemmy, Mbin, etc).
If you wanted to get help with moderating your own community then head over to !moderators@lemmy.world!
Learn more at these websites: Join The Fediverse Wiki, Fediverse.info, Wikipedia Page, The Federation Info (Stats), FediDB (Stats), Sub Rehab (Reddit Migration)
Unless the person replying on Mastodon removes it of course (to save themselves some characters and because they don't recognise it).
There doesn't seem any functional difference between your comment (which implicitly Mentions the community), and the original post on thecanadian.social (which explicitly Mentions it). Screenies from activitypub.academy show that replies to both include both Mentions pre-filled.
https://thecanadian.social/@mike/116234121499688717 didn't remove the Mention, and so the comment made it to Lemmy. https://mstdn.ca/@cass_m/116234270845317774 did remove the Mention, and so it didn't.
Specifically for Lemmy btw, the reply at https://mstdn.ca/@cass_m/116234270845317774 demonstrates another problem - that instance requires a signed GET request for its actors, which hasn't been fully implemented AFAIK.