I think some of that may be caused by the shadow maps being unable to load from RAM limitations (I believe the game has its own RAM limit for textures independent from the computer's). You may want to try adjusting some of the shadow or texture settings to conserve RAM.

I haven't encountered this issue. Try mods like Rendering Improved or Eclipses. If you still get that kind of bug, it may be a hardware issue like Echthros said.

eclipses Is installed on the server Rendering improvements Not