Can’t change gallery settings

Is the nextgengallery 3.3.5 compatible with the Windows Server 2008 R2?
After creating the gallery, I can’t change its settings.
Error message: Gallery path must be located in C:/Server/wp54

After creating the gallery in the table ‘wp_ngg_gallery’ column ‘path’ contains ‘/wp-content/gallery/123qwe/’. If I change it to ‘wp-content/gallery/123qwe/’ from PhpMyAdmin or Manage Galleries page in my browser in the ‘Gallery path:’ field I can change the settings of gallery now. And in table column ‘path’ has changed to ‘wp-content\\gallery\\123qwe/’

How can I change the path by default without first slash?
In settings of plugin on ‘Other options’ page in the field ‘Where would you like galleries stored?’ I have ‘wp-content\gallery\’

Windows Server 2008 R2 + IIS 7.5 + PHP 5.3, 5.6, 7.3 + MySQL 5.1, 5.3, 5.7, 8
Browser: Opera 68, Google Chrome 81, Mozilla Firefox 76
Wordpress 5.4 with new clean site without other plugins, all by default

I tried reset settings of nextgengallery plugin, change theme and restarting my server.

I used version 2.1 before. Path in DB was like ‘/wp-content/gallery/123qwe’ and settings worked.