Hmm, at a glance those all look to be CMR.
To rule this out ideally, a tool like iostat (part of sysstat tools) can help. While moving data, and with the problem happening, if you run something like "iostat 1 -mx" and watch for a bit, you might be able to find an outlier or see evidence of if the drives are overloaded or of data is queueing up etc.
Notably watch the %util on the right side.
https://www.golinuxcloud.com/iostat-command-in-linux/ can help here a bit.
The %util is how busy the communication to the drive is.. if maxed out, but the written per second is junk, then you may have a single bad disk. If many are doing it, you may have a design issue.
If %util doesn't stay pegged, and you just see small bursts, then you know the disks are NOT the issue and can then focus on more complex diagnosis with networking etc.
Awesome, so that's good news. Disks probably just fine.
My next thoughts are on the service itself then... Your service providing the share might be getting throttled or not getting direct access to kernel hooks for performance.
Simplest test I would think is set up Samba or NFS in the host itself, not a container. Try a large transfer there. If speed isn't an issue that way, then something at the container level is hindering you.