i think there was a period early on when the new A320neos often had centre of gravity warnings at the end of the flight and everyone had to remain seated until some of the containers were offloaded from the rear cargo hold. after some software updates that seems to be much less prevalent.

otherwise i haven encountered myself or heard any stories about issues on the A350 (or any aircraft) on departing - and as noted if you wanted to ensure it doesn't tip you certainly wouldn't load the back first if you really did have an issue all that needs to happen is the cargo handlers just ensure they load the front cargo hold first, and the rear one last.