Just adding to this thread for future users' knowledge and troubleshooting.
The reason my users were not getting emails is because Invision turned off all emails from my site without notifying me in any way.
It took me 24 hours to discover this dynamic (and 500 activation emails to new users that weren't sent) and it sounds like the logs were saying the emails were still being sent even though that was clearly not true.
They did this because they felt I violated their "fair use" email volume because I emailed my large user base (200k+) 1-2 times per week to drive usage, promote features, etc. I'm not adding to this thread to complain though I'll need to have a further conversation with them about that dynamic.
Mainly I just want other Invision users to be able to troubleshoot this faster in the future if they run into the same issues.
