samba share open as read only

I would like to open a file as read only which is already open on another computer.
Can this be done?

General input/output error while accessing
is the error I now get.

I thought this used to be possible? What goes wrong/what should I check?

Best regards,

Possibly related to tdf#115747.

This seems to be a problem of early 6.0 version.
In a slightly different setting, it seems to be resolved in