Each product has its own link expiration settings. The link you referenced above is for your item #3, which currently allows up to 3 Attempts. Your free excerpt product (item #1028471) is the only one that currently allows up to 9 Attempts. The product you've been selling lately is item #5, which currently allows up to only 2 Attempts, which is certain to generate complaints about expired links.
We would recommend editing all your products to allow up to 5 Attempts within 120 Hours. Whenever you edit a product's settings, remember to click Next until you can click Submit to apply changes.