Let's encrypt Certs doe not get renewed and cannot be issued

Hi to all,
since several days I'm digging around a Certificate problem. We are using a Windows 2019 Server with Plesk Obsedian V18.0.29_build20200807.15

The renewal of the Let's encrypt certs worked like a charm, since no certificate was renewed about 15 days ago.
Whenever a certificate should be renewed (or created) I got the following message (for all of our daomins):
Could not issue an SSL/TLS certificate for <domain>
The authorization token is not...

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