Hi @auryn and welcome to our community forum!
I have not personally done such a resource intensive configuration on my DAppNode.
Let’s see if someone in the forum can help you, or maybe you can also post this in our Discord to promote it - looks like an interesting case.
Meanwhile I wonder if you have tried to find something in Turbo-Geth logs, or VPN core package logs that may shed a light on what is causing the instability.
Also, you should install DMS, and DAppNode Exporter to have a host and packages monitor system running. Check this tutorial in case you need to: