I'm having the same problem with the collections. I've solved all 16 puzzles but I didn't see a mausoleum piece for a few days. I finally saw ONE today and it was one I already had. I'm at 8 out of 12 for those, 10 out of 12 for alchemy, 3 out of 12 for fish scales and 11 out of 12 for flutes. I keep getting common alchemy and wind flutes. I didn't see a fish scale for the first few days I started playing. I leave the game open for at least an hour at a time so I am actively looking for them.