I think this is possibly crystallised drainage from the eye and the chick is genuinely ill rather than just caked on food. The OP seems upset and considering that they lost a chick whilst trying to treat them and several chicks have closed eyes, I think it is probably more serious than just food on the face. Hopefully they will come back to update us and perhaps post more photos so that we can assess the problem more accurately.
Where are you located? It could possibly be fowl pox if there are mosquitoes out now. Has there been any excessive pecking, possibly injuring the chick. The eye looks weird. What does the other look like?
I don't think anyone is disputing the chick is/was genuinely ill. There is a bit of swelling on the face. I don't think anyone was saying that the problem was just food on the face either. The way the eye looks seems to have been the main topic since it is interesting. I admit it!
It was suggested the chick may have fowl pox. A good possibility. It could also have respiratory disease. The OP has struggled with several issues which seemed to be resolved? but it's very possible that whatever they have been dealing with since summer is now affecting this batch of chicks as well?

If the OP can give more information, that is always welcome.
Were these chicks IB-ND vaccinated?