For posterity, I'm posting the solution. As I suspected, it wasn't really a MWB problem. Vendor installed an SSL proxy. MWB update servers detected that someone had broken the encryption chain and would drop the connection. This affected both signature updates and the licensing traffic. Vendor added exceptions to the SSL proxy on the firewall for the malwarebytes websites to resolve the issue.
I just put one of my small business clients onto MWB Premium for Teams. They have version 3.3.1. Another vendor installed a Fortinet firewall which broke the update process. It seems the AV filter is blocking access to the update site and won't allow signature updates to download. The vendor says there is a problem with the site and put version 2.2 in for testing. Since the problem disappears as soon as they disable the Fortinet AV filter, they've concluded that the firewall must be blocking MWB because of a MWB problem (??). They further claimed that once a problem materializes with version 3.x, it breaks ALL versions of MWB. I don't have access to the Fortinet box directly and it seems they are only logging category level hits on the filters and further details from the firewall are unavailable. Are you aware of any known problems with Malwarebytes and Fortinet firewalls? Is this a test configuration?