System diagnostic suddenly gives me: Found invalid certificate '/etc/univention/letsencrypt/signed_chain.crt'

Apps & App Center
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After changing SSLCertificateChainFile to signed_chain.crt

        SSLCertificateFile /etc/univention/letsencrypt/signed_chain.crt
        SSLCertificateKeyFile /etc/univention/letsencrypt/domain.key
        SSLCACertificateFile /etc/univention/ssl/ucsCA/CAcert.pem
        SSLCertificateChainFile /etc/univention/letsencrypt/**signed_chain.crt**

the command

openssl s_client -connect ucs.<mydomain>.de:443

shows no error anymore.

But yesterday I found out, that Letsencrypt issued new root- and intermediate certificate in September 2020.

I don’t know, how UCS verifies the certificates but it seems, that the validation procedure in the Letsencrypt-App is outdated.