The “revocation information” it refers to is presumably the OCSP status for the certificate.
As a public CA, Let’s Encrypt implements the Online Certificate Status Protocol, which is a web server operated on behalf of Let’s Encrypt that for every certificate serial number can provide a signed, time-stamped message saying the certificate is still good. This is what the “revoke” feature for Let’s Encrypt does - if you know your server was broken into and bad guys might have your private keys, you can revoke them, Let’s Encrypt will then reply “bad” not “good” to OCSP for that certificate (and you can get yourself a new certificate once you’ve secured everything properly).
Alas Windows users get these messages for a variety of inscrutable reasons, I can see reports of this problem dating back long before Let’s Encrypt existed, at least to 2013, so it may be hard to debug. But as I understand it, the most likely include:
The user has the date and time set wrong on their PC. Even just an hour wrong (e.g. from forgetting they moved to a state with no Daylight Savings and left the clock settings the same) can cause trouble. If this is the issue, usually the user will find it works some days but not others, and see the same issue intermittently for other sites too, perhaps at other times.
The user has a firewall or other security device / software that prevents their computer contacting Let’s Encrypt’s servers for OCSP. In this case they would probably see the error also in Internet Explorer browsing https://helloworld.letsencrypt.org/ and they should adjust their system not to prohibit this normal activity.