Pretty Permalinks Not Working Anymore

‘Pretty’ permalinks for the YITH Ajax Product Filter no longer work.

These were working previously just fine, and now serve the filtered results with a plain permalink (../?filter_company=). Previously they would display as (../company/).

I have checked my permalink settings, which have not changed, and every other permalink structure is fine and uses the ‘pretty’ or SEO friendly format – except the YITH Ajax Filtering links.

I do not see any other settings to resolve this behavior, and hoping you can help, as this is impacting my SEO and visitor experience.