Widespread malicious pre-cert Let’s Encrypt cert.chain abuse taking place.
Just a random example: https://host.io/nversia.ru
Also see: https://urlscan.io/result/be1fa059-766a-431d-b879-d04c9cbc73fe/#indicators
Not to say there are website certified there, that are well above board in these respects. 
This particular cert. chaining abuse has been described here:
https://www.mike-gualtieri.com/posts/chaining-remote-web-vulnerabilities-to-abuse-lets-encrypt
Also Ahnlab described it as with: https://asec.ahnlab.com/en/45312/
Hope avast will also flag this kind of pre-chain certstream abuse (use CaliDog to detect).
Wonder whether the sponsors of letsencrypt dot org know,
where part of their money now goes to waste?
Source: luntrus, Bleeping Computer, etc.
polonus (volunteer 3rd party cold recon website security analyst and website error-hunter)