Could not issue/renew Let's Encrypt certificates --> Secure Connection Failed for PLESK admin panel

Hello,
I have configured SSL with Let's Encrypt for several of my domains.
One of the certificates has been configured for the PLESK admin Panel, too.

The renew process of the certificate which is also used for the PLESK admin Panel, failed with the following mail:

Could not secure domains of XYZ (login XYZ) with Let's Encrypt certificates. Please log in to Plesk and secure the domains listed below manually.

Securing of the following domains has failed:
<none>

The following domains...

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