VPS's are unreliable - a resource usage burst can cause all sorts of issues; make sure the clients can comfortable spike CPU both RAM usage, i.e. allocate 2 GB RAM per mirror client (including the OSRS client) excluding the OS resources, and make sure the CPU usage of the mirror client + OSRS client can increase to double the average usage (as observed in the task manager)
Additionally, disable sound on all clients and install a mock sound device if you don't have one - the missing sound device is most common issue on servers and causes memory leaks because the generated audio doesn't go anywhere, runescape requires an audio device as long as you don't disable all game sounds
If the stability of the clients degrades with time that's most likely a memory leak and can be fixed with the mock sound device and disabling audio