I believe there is a glitch that causes you to occasionally swap levels with friends/recommended people, which may explain some things. I made this post a few weeks ago where my 450 (pre-buff) colossus showed as power level 81 for a bit. In the same instance, I received only common/uncommon items (before that change as well) for the first few chests. I found out after making that post that my friend (just on my list, wasn't playing with them or anything) was a level 81 colossus at that time. I know there's other people experiencing a similar issue pretty much permanently, only getting common/uncommon items while doing GM1+ stuff, so possibly related.
Are you still getting into states where you only get whites and greens? I believe we fixed a related bug as part of 1.0.3