I'm no longer puzzled.
Co-in-ci-dence
- They recently added a new firewall [which has been proven partly to blame]
- LE recently changed its' Multi-Perspective Validation [which now includes two new countries]
See: Let's Encrypt is adding two new remote perspectives for domain validation - API Announcements - Let's Encrypt Community Support (letsencrypt.org)
I say:
We were dealing with two problems - that are very similar and just happen to overlap each other in this 60 day renewal period.