Backup failing - "The Content-MD5 or checksum value that you specified is not valid."

[Teiluj]

I have 2 Cloudron servers being backed up to the same local endpoint (S3 API compatible v4)
Historically, this has been pretty stable.
However following updates on the S3 endpoint server as well as cloudron servers (from 9.1.6 to 9.1.7), both cloudron servers are failing with the following error message:

May 03 04:01:22 BoxError: Upload error: code: InvalidDigest message: The Content-MD5 or checksum value that you specified is not valid.
    at runBackupUpload (file:///home/yellowtent/box/src/backuptask.js:192:15)
    at process.processTicksAndRejections (node:internal/process/task_queues:103:5)
    at async uploadAppSnapshot (file:///home/yellowtent/box/src/backuptask.js:359:34)
    at async backupAppWithTag (file:///home/yellowtent/box/src/backuptask.js:382:26)

• Here is the output of cloudron-support --troubleshoot (near identical on both servers):

Vendor: QEMU Product: Standard PC (i440FX + PIIX, 1996)
Linux: 6.8.0-110-generic
Ubuntu: noble 24.04
Cloudron: 9.1.7
Execution environment: kvm
Processor: AMD Ryzen 7 7840HS w/ Radeon 780M Graphics
BIOS pc-i440fx-10.1  CPU @ 2.0GHz x 4
RAM: 16377028KB
Disk: /dev/mapper/ubuntu--vg-ubuntu--lv  117G
[OK]    node version is correct
[OK]    IPv6 is enabled in kernel. No public IPv6 address
[OK]    docker is running
[OK]    docker version is correct
[OK]    MySQL is running
[OK]    netplan is good
[OK]    DNS is resolving via systemd-resolved
[OK]    unbound is running
[OK]    nginx is running
[OK]    dashboard cert is valid
[OK]    dashboard is reachable via loopback
[OK]    No pending database migrations
[WARN]  Service 'mysql' is not running (may be lazy-stopped)
[WARN]  Service 'postgresql' is not running (may be lazy-stopped)
[WARN]  Service 'mongodb' is not running (may be lazy-stopped)
[OK]    Service 'mail' is running and healthy
[OK]    Service 'graphite' is running and healthy
[OK]    Service 'sftp' is running and healthy
[OK]    box v9.1.7 is running
[OK]    Dashboard is reachable via domain name

• There is no relevant information in /home/yellowtent/platformdata/logs/box.log other than the related one above.
• Attempting to add a new backup site result in the following error:

Error put object cloudron-testfile. code: InvalidDigest message: The Content-MD5 or checksum value that you specified is not valid. HTTP: 400

• Cloudron servers can ping the S3 endpoint just fine.

I am wondering what this message means and the best way to troubleshoot this further.