$ php ./proof-of-concept-ISC2-API.php 
Heinrich holds 2 accreditation(s): 
1: CISSP
1311717600 from 
1596146400 until 
2: CCSP
1500588000 from 
1596146400 until 
from 1311717600 to 1596146400

So, yes, it seems to work again

But.. for how long? Oh, come on, there must be some logging or other tracing available that helps a good sysadmin over there find out what causes this.. verification of membership should not result in having to guess what it is: "member is not in good standing" or "member is in good standing but our software is not" ..