I don't know man, maybe they're using Raspberry Pi 3 systems with 1GB of RAM. As far as I know, the mempool data is stored in the RAM.
I dont think it goes offline, it just don't save new transactions. We have a diversity of nodes some may have 32GB of RAM so it's OK. Next time I make a node i will get it 16gb RAM and reserve 8GB for the mempool on clearnet+tor+i2p , problem solved guys
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