Thank you!
I may have found a possible solution. Please note that the search filters can’t be used, as those are not sent along with the ajax request when the sorting is triggered within the filter grid. (that is actually how it should be, so it’s perfectly fine)
Can you please disable all front-end filters, especially the generic filters on the search bar. With the filters the parser would assume that the checkboxes were unchecked and those fields would be disabled. There is unfortuantely no way to technically send that filter data along, as you can have multiple search bars and it would be super hard to tell which data is relevant – overall it would be a mess.
Either way, after disabling the filters it should apply to the filter grid as well, and give you very close results as if the actual live search was used.