Unfortunately at some rare moments, we noticed that the swap file isn't setup properly.
On most cases there is swap memory, but with only 64MB memory.
There is a easy fix for this.
1) Make sure there is no swap usage - if there is, reboot your VPS
2) swapoff /dev/vda2
3) mkswak /dev/vda2
4) swapon /dev/vda2