Bag compression is (I think) often enough the culprit, however in this case I would think more along these lines:
"Soup and a muffin is not very calorie dense, and I suspect that may have been the problem"
An easy way to increase your calories intake there is to add olive oil and or full cream milk powder.
When I was over there I tried the Nido. That was pretty good stuff.
Franco
BTW, I am with the "get a slightly bigger bag than your size" brigade. At 5'7" I use the 6' versions (or a quilt)