Thank you for the pages. I wasn't able to debug the page for precise troubleshooting, but I went through the code and I might have a few ideas you can try to help narrow down the problem and spot the error eventually.
You may try to test the page again, and while doing that have the browser's Developer Tools open. Hit the F12 button when the page is loaded, the Devtools will open, and on the bottom section, you will find a gear icon to change the settings. Click on that and check the checkboxes for the following options, see snapshot below:
I also checked the "Loads.aspx". This page looks like the one that has multiple Grids, but it has no RadSlider. Here, the RadAjaxManager is on the page and many controls are added to its AjaxSettings. This page uses a MasterPage and having that in mind, I would be interested in seeing if the ContentPlaceHolder is wrapped into a RadAjaxPanel or has AJAX enabled in any way through the MasterPage.
Once the page and its functionality are working, you may enable the AJAX which then will prevent refreshing the complete page, instead the Control configured in the AJAX settings will be refreshed only.
Please give these suggestions a try and see if they will help. If you have any questions in the meantime, let me know.
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