>  Я один не понимаю, в чем проблема? Продлите сертификат и все, делов-то.

А новость мы читаем допой, да?

> Five years ago, when Let’s Encrypt launched, that’s exactly what we did. We got a cross-signature from IdenTrust. Their “DST Root X3” had been around for a long time, and all the major software platforms trusted it already: Windows, Firefox, macOS, Android, iOS, and a variety of Linux distributions. That cross-signature allowed us to start issuing certificates right away, and have them be useful to a lot of people. Without IdenTrust, Let’s Encrypt may have never happened and we are grateful to them for their partnership. Meanwhile, we issued our own root certificate (“ISRG Root X1”) and applied for it to be trusted by the major software platforms.
>
>Now, those software platforms have trusted our root certificate for years. And the DST Root X3 root certificate that we relied on to get us off the ground is going to expire - on September 1, 2021. Fortunately, we’re ready to stand on our own, and rely solely on our own root certificate.
>
>However, this does introduce some compatibility woes. Some software that hasn’t been updated since 2016 (approximately when our root was accepted to many root programs) still doesn’t trust our root certificate, ISRG Root X1. Most notably, this includes versions of Android prior to 7.1.1. That means those older versions of Android will no longer trust certificates issued by Let’s Encrypt.

Они  не могут ничего продлить, CA сертифит IdenTrust, которому доверяют старые мобилки, сдохнет в 2021. Поскольку мобилки не обновляются, новый сертификат IdenTrust и новый сертификат LE они не получат.