Mythruna performance shouldn't drop off so quickly that you have to restart every half an hour. That's very strange. I've run it for hours at a time connected to the server... but maybe that's server related.
It may just be my laptop. It was an OK gaming laptop in its' day; about three years ago... But now it's kind of iffy. Mythruna rarely lasts more than an hour without it crashing on my laptop(which is the rationale for my every half hour suggestion). The crashes are much more intermittent on my desktop though, so it may just be the hardware.
Crashes leave an error log. If it's a single player game then it would be nice to see these logs. If it's multiplayer then I imagine the network connection has died... especially likely if you are on wireless, I guess.