well, first what you run is an alpha build, so there are problems with it.
The island world is very demanding, we use it as our benchmark so please turn down your settings in the config app a bit, unless you have GTX980 or Titan
The most important option that has to be switched on is "use half sized resolution buffers" (we will simplify the name later ) that is the performance killer..
About the icons gone, you have the cache, you probably cleared it somehow.. there is also a way to shut down and delete all changes in the world, all the icons you set in it.. it is CTRL+ALT+Q
if you exit spacesys like that, you delete all the icons you set inside.
Can you tell us what is your Windows version?
Soon we will push an update that will run more stable..