If tag slug on Russian language - appears 404 error, when opening archive of this tag.
If open archive of this tag by link from admin panel/tags (view button) - archive opens, if refresh page - opens. But if you open same URL from another place (type hands, or copy/paste url to new window) - archive not found - display 404 error.
I also use same plugin for no category (WP No Category Base) - and all OK with Russian language in slugs.
This problem not on one my site - I have 5 WP on different hostings with same issue.
If delete plugin - URL of tags archive does not return to its original form - site.com/tag/...