Lazy loading products on the catalog pages used to work, but at some point it stopped working and now uses paging. We aren't sure what caused this behavior. Is there a setting that can be changed?
What may have caused this and more importantly how do we get products to lazy load again instead of using pagination?
Do you mean lazy loading or ajax loading? Is "Use AJAX products loading" enabled in admin area > configuration > catalog settings?
What theme are you using?
I checked for that setting, but it doesn't appear to be there. I checked in all settings and the only setting related to that is "catalogsettings.useajaxloadmenu" and "catalogsettings.ajaxprocessattributechange" but they are both set to true.
We are using a custom theme by a company called Foremost Media.
I think nopCommerce does not have lazy loading(no pagination and load products on scroll) of the product out of the box and as I can see you are using NopTemplates Ajax Filter plugin so you can contact their support to report this.