Worm Holes. They could just appear and whisk you off somewhere. Possibly wiping out saves.
Other Galaxies that are are actually VISCIOUS (etc) not just more harsh planets. The Original Elite had Anarchy Systems where a minimum of 4 “really fast” pirates attacked as soon as you arrived and then 4 more etc.
Comets
Meteorites
Meteors.
All can destroy bases/starships/planets.
Planets that really spin or are like Mercury (One side blindingly bright and one utterly dark. Just think. Caves you couldn’t even see right in front of you nevermind Flora and Fauna.