TLDR: Aura v3 will stop working at some point in 2019. Everyone needs to upgrade to v4.
Google is changing their policies for apps which access email inboxes through the Gmail API (but not over IMAP/POP which is a whole other story) and all apps need to go through an OAuth verification process. This is, in principle, a great thing because it’s designed to combat the scammy apps which scrape your data and resell it to the highest bidder.
Aura already complies with all the policies around data access and always has. But during the development of v4 I used a different set of API keys and only v4 has gone through Google’s approval process.
This means that v3 will stop working for existing users at some point. I have already contacted everyone who has bought v3, and am in the process of writing to everyone still using a trial version to remind them to upgrade.
As of April 2019 v3 is still working but I will update this thread when Google does finally shutter API access for older apps.