Sudden backup credentials error for S3 compatible storage (IONOS)

Hi,
I create backups with Cloud Sync Tasks using Backup Credentials.
For that I created Bacup Credentials for my S3 provider IONOS.
That was working fine since a while and my buckets, folders, files got created.

Since some time the backup failed. While investigating this I came to know there is an issue with the Backup Credentials. Whenn I verify my credentials in the UI I get the error
Error: 2025/09/30 18:49:07 ERROR : : error listing: RequestError: send request failed
caused by: Get “<endpoint”: remote error: tls: internal error
2025/09/30 18:49:07 Failed to lsjson with 2 errors: last error was: error in ListJSON: RequestError: send request failed
caused by: Get " ": remote error: tls: internal error.

API Key/Secret Key are correct. I created new keys and used them, but still the error.

Same Keys are working fine in my local Linux system
aws s3 ls --endpoint-url --region eu-central-3
displays the buckets.
( is the real endpoint https address, but here because of forum restrictions for links)

I have no more idea, how to investigate further or what could cause that issue.

Any help is appreciated.
Thanks.

Martin