Costco's brand is usually solid but those spring rolls are the worst for this. The 8 minute mark works if you flip them halfway and give the basket a good shake around minute 4, otherwise the bottom side just steams in its own oil. Also check if your air fryer runs hot, mine runs about 25 degrees over what the dial says, so 400 is really 425 for me. Next time try 380 for 9 to 10 minutes and pull one out to test the crispness before you commit to the whole batch. If they still come out sad, honestly just toss the bag and grab the ones from the Asian market, they're a totally different texture.