Backups suddenly failing - Cannot determine the frame size or a corrupted frame was received

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1

Duplicati - 2.1.0.5_stable_2025-03-04 running on Debian 12 on Intel (real) hardware
Problem already occurred on previous version (probably 2.1.0.1 or older) which I updated to see if it would cure it.
Problem does NOT occur on another Debian machine (using ver 2.1.0.1) backing up to the same remote storage.
Problem apparently started in April, previous backups were OK. Only just noticed the problem due to steadily reducing space on remote storage.
Duplicati is backing up “.chunk” folder of a Proxmox Backup Server (yes, I backup my backups)
The backup starts OK and runs for approx 5 minutes, uploading 4GB of AES files and then fails (see messages below). The following backups do not appear to have cleaned out all the 4GB of failed files.
I deleted the backup completely along with all the backed up files and re-created it. Same problem.
I also tried limiting upload speed to 10MB/s, no difference.
Full log and bug report attached.
Initial warning:

2025-05-21 10:42:48 +02 - [Warning-Duplicati.Library.Main.Operation.Backup.BackendUploader-UploadError]: Error during upload failure: An error occurred while sending the request.
HttpRequestException: An error occurred while sending the request.

Followed by:

* 2025-05-21 10:42:49 +02 - [Error-Duplicati.Library.Main.Operation.BackupHandler-FatalError]: Fatal error AuthenticationException: Cannot determine the frame size or a corrupted frame was received.
* 2025-05-21 10:42:49 +02 - [Error-Duplicati.Library.Main.Controller-FailedOperation]: The operation Backup has failed with error: One or more errors occurred. (Cannot determine the frame size or a corrupted frame was received. (Cannot determine the frame size or a corrupted frame was received.) (One or more errors occurred. (Cannot determine the frame size or a corrupted frame was received.))) AggregateException: One or more errors occurred. (Cannot determine the frame size or a corrupted frame was received. (Cannot determine the frame size or a corrupted frame was received.) (One or more errors occurred. (Cannot determine the frame size or a corrupted frame was received.)))

Any ideas please?
[ETA] “Retry” level debug log added.
duplicati_debug.log.zip (3.6 KB)
Duplicati2Hetzner error log.zip (1.7 KB)
bugreport.zip (1.9 MB)

2

I solved it all by myself!
The culprit was my Realtek 2.5Gb/s USB NIC.
If you are having a similar problem have a look at the output of dmesg | grep enx
If you see something like this:

[ 2154.282777] r8152 2-1.3:1.0 enx6c1ff719fa24: Tx status -71
[ 2154.286261] r8152 2-1.3:1.0 enx6c1ff719fa24: Tx status -71
[ 2154.289741] r8152 2-1.3:1.0 enx6c1ff719fa24: Tx status -71
[ 2154.293400] r8152 2-1.3:1.0 enx6c1ff719fa24: Tx status -71
[ 2154.592577] r8152 2-1.3:1.0 enx6c1ff719fa24: Promiscuous mode enabled
[ 2165.865585] r8152 2-1.3:1.0 enx6c1ff719fa24: Promiscuous mode enabled

Then chances are it’s the same problem.
Not much you can do about it except recompile the kernel with a more recent driver version. I changed to a 1 Gb/s NIC, it was easier.

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