My guess would be a bug in connect for users coming from different instances.
Most likely, @[email protected] was taken to https://lemmy.world/post/837105 instead of https://ttrpg.network/post/837105 …
If that’s the case then that would a bug in how the Connect app deals with absolute vs relative URLs and not something you can fix on your end.

For linking to communities, we can use this format which should work fine regardless of which instance you’re coming from [email protected]

I do not know of a similar way for linking to posts.