Hi,
I have similar or same issue writing to share. I've checked security in both windows and on NAS. As a workaround I was saving to desktop and moving them to NAS with explorer.
Additionally I was having issue getting to the share from open menu, but I am able to get to them from the "My PC" path now. At present there share is mounted using NAS username, that username owns all the files, share is connected with drive letter. If I go to home icon in it shows unnamed folders some of which eventually open as disk and a couple are not expandable. Attached pic of that as well.
Greg