For the Asus users who might be missing context for that change:
About the last 16,000,000 certificates that Let's Encrypt has issued have used this new intermediate:
Let's Encrypt documentation has always advised client implementers to use the certificate chain provided by the CA (so that intermediates can change like this!), but some clients may have hard-coded references that require or assume the old X3 intermediate, in which case they will be broken from now on until these references are removed.