I have wondered about this myself on previous occasions,and usually check first if I get something good from tasks, but with so many things to keep an eye on, and not knowing what you get from a random drop from a tile, or attack on an invader ,especially if you have done multiple attacks, or completed the kill,it makes it much harder to check on stock.

I've had this problem before, I have 100% gotten certain materials from invaders but when checking inventory they were not there. I have contacted plarium only to be told that I never got them. Imagine how many materials you have missed out on over the hundreds of invaders killed. 

This is the topic I was looking for the other day, when I wanted to say , the Hero coffer I found on a tile wasn't in my inventory.