I have a diamond double chest connected to a entangled chest with a vanilla hopper, so when i'm out i can empty my inventory in my entangled bag and fill the diamond chest at my base, my base is chunkloaded.
I don't use that very often, since i have a portable wormhole now, but i realised that at some point the content of the diamond chest duplicated itself.
The last time i used it, i was in the end i guess since i found platinum ingot and voidseeker record, which duplicated.
I tried a few things to reproduce the duplication but can't figure what cause it.