From my point of view, there must be an error in the 9.570 Release when calculating the Uptime. Mine has still 28 days of Uptime, but 9.570 was installed today and afterwards the UTM was booted. This wrong Uptime is shown in the GUI in the Start Page and also in the Mails. See here:
Renewing Let's Encrypt certificate 'zertifikatsname' has failed.
Reason for failure: An error occurred while communicating with the Let's Encrypt server.
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System Uptime : 28 days 1 hour 53 minutes
System Load : 0.33
System Version : Sophos UTM 9.570-20
Please refer to the manual for detailed instructions.
Did anybody else face this issue as well?