Plane rolls to the right at high altitude

[i like turtles]

So I just made a Sukhoi PAK-FA replica and I test flew it. It flew fine until about 8000-9000m altitude when it violently rolled to the right, and it was hard to control it until down to 5000-6000m altitude. I can't provide pictures for now, as I'm overseas. I will post a picture/gif when I'm back. For now I just want to know if anyone knows what's happening and how to fix it.

[James Kerman]

Due to the fact it's pulling to one side or the other it sounds like an asymmetrical flameout - one engine is starved of air.  You can test this by monitoring the airflow into the engines when getting to the problem altitude.

[bewing]

A craft file would be even more helpful here. I assume you mean that your gaming PC and you are separated by an ocean now? So when you get back.