XP Gain and disappearing Uniques

[Morhem]

So I started on max difficulty - already regret that decision immensely - hunger/thirst is obnoxious, but manageble, but save/quicktravel restrictions is just.. ugh. Anyway, thats not what I wanted to ask. Here's the situation:
I'm lvl 3, and did a manual save on the ship, planning to go out, and kill Orthrus (unique canid with tons of loot and XP). So I go, clean a couple of enemy locations, visit a couple locations that give XP for visiting (volcano, cargo container), and boom - I'm lvl 4.
I go kill Orthrus like I planned, loot a cool gun from him, and then proceed to die to some marauders. Happens. Anyway, I reload, repeat the same trek - but no Lvl this time, and in fact, XP bar barely budged! Why? What happened? That's the first part of my question.

On to the next: This time, Orthrus kicks my butt, and I decide to prepare. I clean nearby lairs, and loot a few buildings, finding a plasma rifle - nice. Go back to the ship, save, go back to Orthrus... and he's not there. Just gone.
I reload before I looted plasmagun - Orthrus is there. I loot the plasma - he's there, but I want to save first. I go save, and he's gone.
What's the deal? Is looting a plasmagun some kind of trigger for him to vanish into thin air?
What's the message here? That I'm only supposed to go where compass tells me? Or the game will punish me by taking away loot and xp? What is happening here?

[Marquise*]

Not sure. Ever since I've installed DLCs, ADA seemed to stop reporting my crew-mates and for some reasons I get troubles getting reputation working with factions. It is extremely annoying.

Hope you didn't get those. Maybe report on their site. :S