I only read this about a year ago but I was on a heavy reading binge and a lot of the details have got lost amongst other stories.
Basic points: Earth (and her offshoot colonies) are playing off 3 or 4 hostile alien empires against each other but suspicions are forming with the main alien species.
A female space navy ship captain suffers a series of jump point mishaps and finds herself in an uncharted star system through a lot of hidden wormholes. One habitable planet, somewhat bleak but liveable. On landing they rescue some crashed guy who's been there for a while, all make it back to Earth society and reunite with their respective alliances.
The hostile aliens do a bit of treachery and suddenly most of mankind is wiped out with survivors in scattered ships all over the galaxy. They join together and, as they're quite heavily armed, they negotiate a route out of the enemy zones with an alien/human summit meeting and all seems fine.
However they know it's an alien plot to ambush them en route, so they do some jump point double bluffs and manage to follow the charts to the isolated bleak planet. This jump series leaves the aliens without a clue and they follow a false trail that goes way way out.
The human fleet emerges above this dull brown world (dominant plant is moss, not grass) and know this is their chance to rebuild humanity, they agree that, as it represents freedom and life, this planet is beautiful.
Thinking back, the mystery book could be first of a series (speculating only)