Permission denied when trying to access Docker volume mounted to host machine

Hi,
I use WinSCP to connect to an Ubuntu machine running Docker. I would like to use it to access mounted volumes like /var/lib/docker/volumes/xyz_capture/_data

1. I had it all sorted out and working but then I upgraded WinSCP version and lost it. No clue what I did to make it work and nothing I do now solves it.
2. I login to WinSCP using the regular user. The docker volumes require SUDO to open.
3. I've seen these posts:
a) https://winscp.net/eng/docs/faq_su
b) https://raspberrypi.stackexchange.com/questions/74011/how-can-i-connect-to-the-sftp-server-with-sudo-via-winscp
c) https://stackoverflow.com/questions/34798936/how-to-run-sudo-command-in-winscp-to-transfer-files-from-windows-to-linux

But none of the solutions worked for me (do not want to try to login as root or remove passwords, etc.)

It seems to me so basic requirement that I wonder what am I missing here that is so obvious :(

Any help will be highly appreciated as current situation slows my work significantly (I need to download files using SSH from the Docker volumes in order to open them locally).

Thanks in advanced!

While it may seem as a basic requirement to you, it's not an easy task, as there's no support for "su" in any file transfer protocol. So the problem is actually non-trivial. It's all summarized in the FAQ you have yourself posted:
https://winscp.net/eng/docs/faq_su

There's no better solution than what is listed there.

We unfortunately cannot know what approach did you take before.
By upgrading WinSCP you should not have lost anything. Settings are preserved. No relevant functionality was ever removed.

If none of the options from the FAQ work for you now, something must have changed on the server, not in WinSCP.

Thanks Martin for your prompt reply.
I might failed with the terminology of defining it as basic. My apologies. Maybe a better phrase will be 'required by so many'..

Anyway, I assume new versions should not change former settings. Even on portable versions (the one I use), right? Can you tell me where can I find the past versions cached data? Something like ...Users/[user name]/AppData/..? Or am I shooting at the wrong direction?
It is just that I think it is not something on server as I have 3 of those, all stopped supporting it at the same time - right after the upgrade.

Thank you very much for your support.

See https://winscp.net/eng/docs/config

So did you have a stored site that when connected before allowed you to manipulate those files? And now the same site does not? Or did you lost the stored site? We need to know more about what you are actually doing.

See https://winscp.net/eng/docs/config

Thanks.

So did you have a stored site that when connected before allowed you to manipulate those files?

Yes.

And now the same site does not?

Correct.

We need to know more about what you are actually doing.

I understand. the problem is that the old setup was done long ago (maybe 10 months..) and when I finally upgraded WinSCP I didn't forecast this problem so it took me time to notice it and I'm not sure what I did before.

Please attach WinSCP session log file.

If you downgrade back, does it start working again? If it does, please attach log file from the old version too.

Hi Martin, took me a while but now I have available also a machine that used to have access to the docker volume and still has. So the situation is the following:
Two identical machines (HW wise) with same Ubuntu server OS (latest official). Not updated to the same latest updates. User has the exact same rights on both machines:
Latest WinSCP.
Same log-in settings being used for both.

With one machine I can access the Docker's volumes while with the other I cannot.
As the user has the same rights on both as well as the same groups exists and same /etc/passwd, I with my very limited Linux knowledge, don't have a clue where to look for the problem.

Regarding the logs – I have enabled the logging but feel reluctant to paste them here publicly. Is there a way I can send them to you in private? (That is if you still need them)

Thanks in advanced.

--- UPDATE ---
I had to update the packages on the machine that used to work. Now it doesn't. So it is clearly not a WinSCP issue but something either on the Docker or the Linux itself.
I understand it is beyond the scope of WinSCP, but any help will be highly appreciated.
Thanks.

Consider posting your problem at https://superuser.com/ or https://serverfault.com/.

Post a link here, if you do.

Here it is:
https://superuser.com/questions/1697213/accessing-dockers-volume-using-winscp