In ATM7 0.4.15, whenever a player (un)loads a chunk or changes dimensions, the old data is kept in their client's heap indefinitely. This can build up over the course of several hours and kilometers of exploration and eventually lead to a crash with java.lang.OutOfMemoryError as many ClientLevels are kept, filling up the heap memory but not being accessible or able to be freed by the GC.

• This does not happen in vanilla.
• The specific mod combination causing the memory leak must be present in both ATM7 0.4.15 and FTB Direwolf20 1.2.x, since I get a similar memory leak in both modpacks.
• This issue is present since at least ATM7 0.3.22 and likely earlier.
• The memory leak occurs on both long-distance travel and changing dimensions. In addition, every time a player stays in the same dimension for a few minutes and then enters a portal to go to another dimension, their client's heap memory usage permanently increases by around 1-5% (based on render distance), assuming the maximum allocation was 6 GB.

What mods may be causing this memory leak?

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Try removing the following mods:

• FTB Chunks
• Journeymap
• Journeymap Integration

Instead, replace them with the following:

• Open Parties and Claims, if you desire the claims feature from FTB Chunks.
  • If you need to claim stuff for the forceloading part only, there's the vanilla /forceload command and a couple of different blocks and entities in the pack that forceload the chunks they're in.
• Xaero's Minimap
• Xaero's World Map

This should reduce memory usage and improve performance, though I have not tested that combo on a long continuous session of exploration yet.