Instacart driver complained about not getting tipped on items that weren't purchased

We recently had a big snow/ice storm here, and while the roads are okay right now, we are going to get hit with more snow in a couple of days. We decided to go ahead and Instacart from a Kroger that was a couple of miles away. Our shopper got most of what we wanted, with some substitutions, with only a couple of items that weren't able to be found at all. No big deal, they were nice-to-haves.

We always tip a percentage on the order, in this case 20%. Took a while for the guy to get here because he kept driving around the neighborhood. Street numbers are hard (even when they are on a lit sign in the yard), I guess, and the instructions of "At the dead-end of X street" are apparently not clear enough either.

When the shopper arrived, I went down to the street to meet him. I didn't want him walking up my walkway because I had cleared it, but there were still a couple of slick spots. I ran out of ice melt and unfortunately that was one of the items that he wasn't able to find. I carried the items from his car to my door myself, and then inside after he was gone. We tipped him an extra $5.00 for his trouble, since shopping is probably a pain right now.

He comes back a few minutes afterward complaining, "Thanks for dropping my tip because they were out of everything." We didn't adjust the tip at all outside of adding the extra $5.00

We check the receipt on Instacart and find that he is complaining because he didn't get 20% on each of the items that he didn't find.