Resolved:

Reddit itself doesn't filter. Reddit HFY does.

It is not possible to link from Reddit HFY to Lemmy HFY directly due to shadow-filtering. The whole message with the link will be only visible for the creator. Working around with eg https://lemmy(dot)world/post/94994 though works as long as the user edits the link while copying it.

old text

Does Reddit block Links to Lemmy.World?

I just wanted to post a link in a Reddit Answer. To my utter surprise the message was not shown to other people. I as the author could see it without any hint it would be invisible.

But everyone else couldn't see it. It just wasn't there, even an direct linkt didn't help. Editing the message didn't help either. I had to delete it and rewrite it without mentioning "lemmy.world" in the message.

Here is a workaround where I avoid a link and it works:

Reddit Post without Link Workaround

Reddit Post with Link

Edit 1: To make myself clear again, you should see at least one message without a link and one with a link to Lemmy. But you will only see the one without a link. The trigger seems to be the exact word “lemmy.world”. Is that a known problem?

Edit 2: Wow, this goes deeper. A fresh Edge browser does show the link post. A old Edge browser doesn’t. All browsers with strict privacy settings don’t show the link. Firefox in Private Mode and with Adblock doesn’t show it. Edge and Chrome in private mode don’t show it either. A fresh chrome doesn’t show it. An older Installation of Chrome does. Reddit is doing something very strange.

Edit 3: https://lemmy(dot)world/post/3375662 seems to bypass the filter. So it is true: Reddit filters their biggest competitor.

Edit 4: The Shadow-Ban doesn't seem to work on r/help but definitely on r/hfy.