There’s no such thing as ‘saving to RAM’. All functions in MineOS–all of them–save to the filesystem.
Likewise, when you make backups (“restore points”), they save to /var/games/backup/servername.
Java at times can seem bad at housekeeping, but actually more often it’s Minecraft/mods’ fault for leaking memory; the amount of work put in to making Java work properly absolutely dwarfs the amount of time and effort put into testing Minecraft and third-player mods.
One other thing…sometimes the MineOS webui starts ballooning in memory; this is caused by enormous worlds and using old commits.
But we can’t know without more information. In the command line, use the command top which will actually list where all the memory is being used–if it’s Java/Minecraft, then you just need to restart your Minecraft servers (or potentially your host system if it’s a bad leak).