In my personal head canon Trazyn spends his free time gallivanting across the galaxy saving the day just because nobody expects some Catachan Devils (the beasts, not the soldiers) to show up out of nowhere on a desert world. Yes, a good quarter of that IG regiment was brutally slaughtered after their release, but that's better than losing the whole thing to the foe they were facing. Hell, he's the kind of guy who would stop a Chaos plot in the heart of the Imperial palace that threatened to wipe out all of mankind by dropping in a Catachan Barking Toad and killing everyone, and then announce his presence and boast about how he beat the Imperium at their own preferred problem solving technique of killing everyone and everything present.
What's the Imperium going to do about it, admit anything resembling the truth? Na, they'd just cover the whole thing up, say there was a plot of no real consequence, that wing of the palace is completely uninhabitable because of a completely unrelated plasma leak, and that nobody should look into things further.