Really important that you try and take note of the detail of the map next time it happens… especially if you were not even using skills/fighting mobs…
Just a note specifically for your setup - Have you tried to dial back the in-game settings from Ultra to lower quality? Ultra settings have been known to cause problems - even on high end machines and it could be that something enabled in Ultra mode on the new 0.8.3 patch is also affecting this… Just drop it to High or lower and see if it makes any difference - just as a temporary test…