Let’s Encrypt communicated on March 2 2020 that they will revoke a part of their certificates . CAUTION: the certificates will be revoked from March 4 2020 0:00 UTC onwards. The certificates that will be revoked have been issued BEFORE February 29 2020 03:10 UTC. According to Let’s Encrypt about 3 million certificates will be revoked, of in total 116 million active certificates . The reason for this revocation is a bug found in their CA software .
Source: Read More (National Cyber Security Centre – News items)