Have you identified any memory leaks yet?
In the beginning I had over 200MB free on my node with 512MB RAM, but after running for some time it was only around 45MB free. At the same time it also started to miss forging more and more blocks, so I had to restart it.
I use to see this on the smaller 512MB nodes from DO during testing. I would recommended upgraging to a 1gb node, and if your still seeing this issuse I would move from DO. The only thing I could ever come up with was its how they partition the Ram on the servers. I'm running 10 nodes right now, 3 of them are at DO and are 1gb each. They are running just fine and have double forged in many rounds. They don't use more then 300MB tops. For some reason its how they have the servers set up, 300MB on a 512MB is not the same as on a 1gb. I hope this helps, please keep us up to date on what your seeing. Thank you for your feedback