You're viewing a single thread.
If you are subscribed to the same mag 3 times, well it's on you. You want volume you have it.
What is possible is to filter through a script and only show the local one.
A possibly nice UX could be clients grouping all crossposts from the same author together in a little stack, but showing the local or oldest version "on top"
Initially I thought you were saying they subscribed to a single magazine from the same instance three times and was thinking "Is that even possible?".
Then I had a closer look and realised they were 3x different magazines on different instances but all with the same name.
Makes sense that it would appear 3x times.
I'm hoping eventually there will be a 'merged' view for this situation, so all the comments are amalgamated, and the article appears once only. Whether that can happen server side or will need to be an app-specific feature, I guess time will tell.
Since instances tend to be generic, this will only get worse over time.