Peter Schlager

Excellent choice. I’m running a physical Routerboard and a virtual RouterOS inside my hypervisor for redundancy.
The license for virtual RouterOS is dirt cheap and has more features than you could ever dream of with any of the the big network device manufacturers.
The physical devices are very well designed for their relatively modest price and likewise fully featured. Perfect for any home lab or to play around with IEEE conform protocols.

You’re quite bold - I like it ;-) in all honesty, is your requirement mounting an NFS share? As indicated by @chris it really is designed for the local network.
How about using something more suited like a WebDAV share/mount?

I don’t see a clear indication that you have too low RAM… RAM should be “used” fully at all times and your “cached” RAM value suggest you still have quite a bunch of RAM that could potentially be consumed by applications when they need it.
I cannot clearly see a swap usage in the graphs - that would be an interesting value to judge the overall stability of the system with regards to fluctuating RAM usage.

However, once you notice the problem again, right after you manage to log in, run a “dmesg -T | grep -i oom” and see if any processes get killed due to temporarily spiking RAM consumption. If you’re lucky that command might lend some insight even now still.

Also, what if you run a “top” command for a while, what’s the value for “wa” in the second line like? “wa” stands for I/O wait and if that value is anything above 5 it might indicate that your CPU is being bottlenecked by for instance hard disk speed.