Server memory management problem/leak? on amplified

Exploring the world on amplified quickly leads to the server using all of it's allocated memory and slowing down significantly (re-appearing blocks, players waiting for up to 15 minutes in front of the void to load the chunks), chat works fine. I guess amplified "requires a beefy computer", but the server using all 12 GB of allocated memory with 4 players on it after some time seems to be an issue.

I'm playing on a friend's server, and the issue came up, as I said, after some exploring with 3-4 people and 12 GB of allocated memory (16 total on that machine, but it was staying idle apart from the minecraft server at that time). On a dedicated server with 8 GB allocated it came up much faster. I've also tried it on singleplayer and the world would stop generating completely after flying a couple hundred blocks from spawn (with 4 GB allocated on an 8 GB machine).

The problem occurs both when generating new chunks and when loading existing ones