This was reported on dspace-tech:
In dspace 4.0, mobile theme: http://mobile.demo.dspace.org/xmlui/discover
When i search in mobile theme, cannot click link Title Asc, Tile Desc....
Link when click Title Asc: http://mobile.demo.dspace.org/xmlui/sort_by=dc.title_sort&order=asc
This is wrong link, correct link is: http://mobile.demo.dspace.org/xmlui/discover?sort_by=dc.title_sort&order=asc
The reason is that the mobile theme doesn't take into account the sort options (see attached screenshot), which show up as a gear icon in Mirage in DSpace 3+. Templates to render them appropriately for the mobile theme need to be added.