1) No spam was received since the previous quarantine report was sent.  This isn't super common, but we do see it happen from time to time with email addresses that don't get a lot of email traffic to begin with.

To verify if this is the issue, login to the SpamHero control panel and take a look in the quarantine to see if any spam has been received since the last quarantine report was sent (and before the time the next report was supposed to be sent).  It's easiest to login directly to the quarantine account in question, but you can also use the shared quarantine and look for spam sent to the quarantine user's email address.

2) Your mail server is blocking the messages  or they are landing in the junk folder in your email software (very common). It's also common for your email software to put Quarantine Reports in your spam folder. 

To verify that quarantine reports are still being delivered, find the most recent Quarantine Report via the Quarantine+ > Quarantine reports tab, then click the Quarantine report delivery status link:

Quarantine report logs

Examine the delivery logs to obtain the needed tracking information to see what your mail server is doing with the quarantine reports:

http://www.SpamHero.com/support/88033/View_raw_mail_delivery_logs_for_clean_messages.php

To ensure delivery of your quarantine reports:

1) Add noreply@spamhero.com to your address book in your email software.  Note: If you're a reseller, the address to add is noreply@[YourResellerDomainHere].   If you're using a hosted mail solution then sometimes this is all you need to do.

2) If possible, whitelist the SpamHero IPs on your mail server (may not be possible if you're on a shared mail server):

http://www.SpamHero.com/support/78972/Current_List_of_SpamHero_IPs.php