Defina a opção padrão no menu suspenso do php e retenha quando a consulta for enviada

while ($row = $result->fetch_assoc()) {
         $nx_version = $row['nx_version']; 

         if($_SESSION["id"])  {
           if($nx_version == "the hardcode value you want to be selected"){
              echo '<option selected="selected">'.$nx_version.'</option>';
           }else{
              echo '<option>'.$nx_version.'</option>';
           }
         }else{
           if($print_version1[array_keys($print_version1)[0]] == $nx_version){
             echo '<option selected="selected">'.$nx_version.'</option>';
           }else{
             echo '<option>'.$nx_version.'</option>';
           }
        }

 }