There's a lot of chatter on the Zazzle forum regarding referrals diminishing 'overnight'. There was a change made and it could well be the reason? Speculation only meanwhile as we can never really know for sure without Zazzle confirming the details.

Zazzle’s referral tracking lasts forty-five (45) days, with a rolling fourteen-day (14-day) lockout period during which other referral clicks won’t override your attribution.(help.zazzle.com)

In simple terms:

• Once someone clicks your referral link, you’re credited with any sale they make up to 45 days later.

• For the first 14 days, your link is "locked in"—even if they click someone else's referral link, yours stays valid.

• After day 14, if they click a different referral link, the new referrer gets the credit for any future purchases.

Cookies are around for 45 days same as before the difference is there's a new lockin rule

• Once someone clicks your referral link, you’re credited with any sale they make up to 45 days later.

• For the first 14 days, your link is "locked in"—even if they click someone else's referral link, yours stays valid.

• After day 14, if they click a different referral link, the new referrer gets the credit for any future purchases. 

I wonder if 'new referrer' includes Zazzle itself as a referrer?

If it does then I think we need to accept the 14 days might be the new normal ... unless the Pepperjam/Ascend affiliate program ( I'd have to check as I've been away from all things Zazzle for a long time) is still running in which case the rules for that might be different.