You are right, not slugs. I put my raspberries between the compost bin and the rest of the garden. You normally get bad slug damage within eight feet of a compost bin, but they don't touch raspberries. Looking at the holes I wonder about something like a leafcutter bee? On the other hand there seems to be more damage at the bottom of the plant. It does look as though it is getting big for that pot, you could try re-potting it in something a good bit larger and replace the top layer of soil. If you scrape off the top and replace it with something like a two to one compost manure mix, or compost with blood and bone, it is a good way of cleaning out undesirables and feeding the plant at the same time.