Sorry this is causing you some trouble. It looks like technically the widget is doing what it’s coded to.
Unfortunately sometimes when setting the window.location.href value it appends instead of sets. I believe that’s what you’re experiencing.
There’s a way to fix this that doesn’t involve changing the code of the widget. You could create a deep link that will make the user sign out and then redirect them to a different page. I know it’s a lot of jumps for the user, but if they’re going through this logic they’re either idle or logging out anyways. After creating the deep link you would use the deep link’s path as the redirect URL in the widget configuration and this should get you the functionality you’re looking for.
If you do feel comfortable maybe creating a fork of Kinetech’s widget code and updating it, you could go that route too. You’d just need to edit lines 110 and 115 of their SessionTimeout.js to be something more along the lines of the answers in this SO post: JS Redirect Solution
Hope this helps!