Simple way to enable MTP file transfer on Galaxy S2 (Replicant 6.0 0003)?

When I plug the device and enable MTP transfer on it,
I can see and navigate into the file system.
But there's no way to copy/paste a file (libmtp issue, something like failing to answer).

I even tried to revert back to Replicant 4 (where it worked fine, but maybe it was USB Mass storage),
but it failed, so I reinstalled the latest version.

I installed and tried jmtpfs and go-mtpfs. I created a folder to mount the devices file system on.
The first one got the device once, but no way to navigate into the folder.
I could on the CLI, but no way to ls its content.

Btw, I'd like to use a strictly offline solution.

Thank you for any input.