Our webhost upgraded PHP, so we had to upgrade our EE install from 2.7.3 to 3.5.2. With that process we also upgraded the Solspace User module from 3.4.5 to 4.0.8. PHP is now at 5.6.21 CGI(Stable).
New registrants must be manually approved by the admin. In the older version of EE, when you approved a member, there was a "send member activation email" box we had to uncheck because it would send both the User welcome email AND the default EE activation email, which we didn't need.
Now that box/option is gone, and approving the member does not kick off the User welcome email. The user receives nothing. I verified that "Notify Members When Approved" is set to yes. [EDIT: previously I posted that the default EE activation email didn't arrive either, but it finally did. So the normal EE function is working.]
Is there something about the new PHP that could be tripping things up, or does EE3/User4 expect PHP 7 (which we can upgrade to if needed) ?