This same thing started a few weeks ago for me as well. I have a cron job that parses my log file and sends me usage statistics every morning. I had been receiving this email for 100+ days when suddenly it stopped. I investigated thinking it was a problem in my script only to find that all worked well and all emails were in my spam.

I use SES from AWS and now my new user sign ups emails for email verification also end up in spam. It’s very frustrating because they changed some rule and now my low volume email sending is considered spam