Hazmat STA early expiration?!?

Alright I am an enrollment agent for an UES center, not a cdl carrier.
I have been getting lately several applicants in for a HME STA with current endorsements on their license, but are informed via their employer or a letter in the mail about the STA expiring early. For reference, no names, but one person had his license less than a year and his license expired in 5 months. Another had it for a couple of years and didn't expire for 3 more years. These examples are from different states on different coasts.
So my questions are how wide spread is this? Is this due to the Federal Compliancy regulation for flying? And are there any other TSA employees who can corroborate this for our Transportation servicemen?

 

Both examples had CURRENT licenses and CURRENT HME STA’s but were notified to get another STA or their hazmat would be invalidated.