After having the same experience of 'not seeing' the 'Add Path..' button, I started looking inside the code of the "Web UI in PHP" which you are probably running on the NAS.
With very little experience in HTML, PHP, etc. I think I happend to find the answer.
Step by step:
1. With the normal File Station on your NAS you go to the following folder "web/serviioweb/view"
2. Inside this folder there are different .php files. Look for the 'Library.php' and download that to your Mac/Windows/etc.
3. Open the library.php file with notepad or any other 'HTML/PHP/XML-editor'.
4. Press 'ctrl-F' (which opens the search bar) and search for 'AddPath'.
5. You should see the following search result:
- Code:
........?php echo tr('tab_folders_button_add_local','Add local...')?>
</button>
<!--
<button type="button" id="addPath" name="addPath" class="ui-button ui-widget ui-state-default ui-corner-all btn-small">
<?php echo tr('tab_folders_button_add_remote','Add path...')?>
</button> onclick="addLibRow('libraryTableFolders',null)">-->
<button type="button" id="removeFolder" name="removeFolder" class="ui-button ui-widget ui-state-default ui-corner-all btn-small" />
<?php echo tr('butto.........
6. As you can see, the <button type="button" id="addPath".....null)"> is in between comment tags ( <!-- [HTML or text] -->).
7. Also, the 'onclick' event was placed outside the button tag. I also changed that, so that the onclick event was inside the button tag.
8. These changes resulted in the following code:
- Code:
<button type="button" id="addPath" name="addPath" class="ui-button ui-widget ui-state-default ui-corner-all btn-small" onclick="addLibRow('libraryTableFolders',null)">
<?php echo tr('tab_folders_button_add_remote','Add path...')?> </button>
9. Select the code in between the comment tags (also select the comment tags) and replace that with the code in step 8. So, change "<!-- <button type=.......null)">-->" with "<button type=..[step 8 code]..</button> ".
9. Save the Library.php (do not change the name) and upload it to the NAS on the following location: "web/serviioweb/view" (be sure to override existing files, otherwise it will not replace the excisting library.php).
After this adjustment, you should be fine and the 'Add Path..' button should be there.
Hopefuly my guide is clear, otherwise let me know.
NOTE: I am a tech novice and just started working with html/php/etc. So if something is wrong with this adjustment, please let me know.
Regards and good luck!
PS I will also post this in the "Web UI in PHP" section as I think the problem lies with that 'third party application'.