[schapplm]

Finally I was able to look into the SMB+Windows issues that were reported for a few months now and was able to reproduce them:

From github (Sep. 2017): I have Kodi installed from the windows store on Windows 10.. The SMB path for the db file doesnt work on windows... I tested SMB paths on android and it works fine... says Can't access file at \SMBpath\path\watchedlist.db (I changed the path names but I know they are correct on my settings).

I moved the watchedlist.db to my SMB share and pointed the addon at it. It says "error opening WL_Database"
Is this still an issue that hasn't been resolved or can this not be pointed at an SMB?

I have the same problem (on Windows 7).
Is there a fix (that is not using mysql)? It works via a mapped network drive, but that is problematic for me for other reasons.
[...]
Of course, the path \\SERVER\Kodi\WatchedList\ does in fact exist, and I can access it in Windows.

 
Unfortunately, my own tests seem to date back a little.

I used NFS but I also tested this with SMB network shares before. Perhaps you also have a corrupted database file already in your userdata folder.

It seems that this already stopped working between Kodi 12 and 13.

The problem was, that the support for the backslash-notation for windows network shares (\\server\share) is not supported (unofficially) any more. Also the syntax smb://user:password@server/share was not translated correctly by my addon. I submitted a fix which should be available in the next week. Please let me know, if the problem still persists after the update to addon version 1.2.5.

As for SMB problems on Android:

Since mid decemebr I have not been able to get the addon working on a SMB share, it was working properly before that. This happens on the 3 android TV devices that I have tested.
Another add-on (Backup) works fine over SMB on the exact same shared folder and cleaning/changing/renaming the destination folder does not work.

I did not have any idea how to solve your problem yet. It is probably not a general Unix+SMB problem, since it seems to work on some machines. I am not sure how your configuration would be different from mine or others. So I do not think my update will fix your problem.
Edit: One final thought. Eventually this is a permissions problem after all. It is possible to store the smb credientials (username and password) for shares globally in a configuration file and access the share with smb://server/share or one can set the username and password also in the path like smb://user:pass@server/share. Did you try both ways? On my system (Ubuntu 14) I had to type in the password to get access.